Issues compiling OF, getting "previous declaration" errors

gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
mesa-common-dev/bionic-updates,now 20.0.8-0ubuntu1~18.04.1 amd64 [installed,automatic]

I tried v11 as well as nightly build. Same result.

I keep getting these compile errors, and havent been able to find a solution. Any insight?

In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12306:105: error: conflicting declaration 'typedef void (* PFNGLFRAGMENTLIGHTFVSGIXPROC)(GLenum, GLenum, const GLfloat*)'
 typedef void (APIENTRYP PFNGLFRAGMENTLIGHTFVSGIXPROC) (GLenum light, GLenum pname, const GLfloat *params);
                                                                                                         ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16092:28: note: previous declaration as 'typedef void (* PFNGLFRAGMENTLIGHTFVSGIXPROC)(GLenum, GLenum, GLfloat*)'
 typedef void (GLAPIENTRY * PFNGLFRAGMENTLIGHTFVSGIXPROC) (GLenum light, GLenum pname, GLfloat* params);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12308:103: error: conflicting declaration 'typedef void (* PFNGLFRAGMENTLIGHTIVSGIXPROC)(GLenum, GLenum, const GLint*)'
 typedef void (APIENTRYP PFNGLFRAGMENTLIGHTIVSGIXPROC) (GLenum light, GLenum pname, const GLint *params);
                                                                                                       ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16094:28: note: previous declaration as 'typedef void (* PFNGLFRAGMENTLIGHTIVSGIXPROC)(GLenum, GLenum, GLint*)'
 typedef void (GLAPIENTRY * PFNGLFRAGMENTLIGHTIVSGIXPROC) (GLenum light, GLenum pname, GLint* params);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12310:96: error: conflicting declaration 'typedef void (* PFNGLFRAGMENTLIGHTMODELFVSGIXPROC)(GLenum, const GLfloat*)'
 typedef void (APIENTRYP PFNGLFRAGMENTLIGHTMODELFVSGIXPROC) (GLenum pname, const GLfloat *params);
                                                                                                ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16088:28: note: previous declaration as 'typedef void (* PFNGLFRAGMENTLIGHTMODELFVSGIXPROC)(GLenum, GLfloat*)'
 typedef void (GLAPIENTRY * PFNGLFRAGMENTLIGHTMODELFVSGIXPROC) (GLenum pname, GLfloat* params);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12312:94: error: conflicting declaration 'typedef void (* PFNGLFRAGMENTLIGHTMODELIVSGIXPROC)(GLenum, const GLint*)'
 typedef void (APIENTRYP PFNGLFRAGMENTLIGHTMODELIVSGIXPROC) (GLenum pname, const GLint *params);
                                                                                              ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16090:28: note: previous declaration as 'typedef void (* PFNGLFRAGMENTLIGHTMODELIVSGIXPROC)(GLenum, GLint*)'
 typedef void (GLAPIENTRY * PFNGLFRAGMENTLIGHTMODELIVSGIXPROC) (GLenum pname, GLint* params);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12319:104: error: conflicting declaration 'typedef void (* PFNGLGETFRAGMENTMATERIALFVSGIXPROC)(GLenum, GLenum, GLfloat*)'
 typedef void (APIENTRYP PFNGLGETFRAGMENTMATERIALFVSGIXPROC) (GLenum face, GLenum pname, GLfloat *params);
                                                                                                        ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16101:28: note: previous declaration as 'typedef void (* PFNGLGETFRAGMENTMATERIALFVSGIXPROC)(GLenum, GLenum, const GLfloat*)'
 typedef void (GLAPIENTRY * PFNGLGETFRAGMENTMATERIALFVSGIXPROC) (GLenum face, GLenum pname, const GLfloat* data);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12320:102: error: conflicting declaration 'typedef void (* PFNGLGETFRAGMENTMATERIALIVSGIXPROC)(GLenum, GLenum, GLint*)'
 typedef void (APIENTRYP PFNGLGETFRAGMENTMATERIALIVSGIXPROC) (GLenum face, GLenum pname, GLint *params);
                                                                                                      ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:16102:28: note: previous declaration as 'typedef void (* PFNGLGETFRAGMENTMATERIALIVSGIXPROC)(GLenum, GLenum, const GLint*)'
 typedef void (GLAPIENTRY * PFNGLGETFRAGMENTMATERIALIVSGIXPROC) (GLenum face, GLenum pname, const GLint* data);
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12323:74: error: 'void __glewFragmentColorMaterialSGIX(GLenum, GLenum)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentColorMaterialSGIX (GLenum face, GLenum mode);
                                                                          ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19341:52: note: previous declaration 'void (* __glewFragmentColorMaterialSGIX)(GLenum, GLenum)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTCOLORMATERIALSGIXPROC __glewFragmentColorMaterialSGIX;
                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12324:84: error: 'void __glewFragmentLightfSGIX(GLenum, GLenum, GLfloat)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightfSGIX (GLenum light, GLenum pname, GLfloat param);
                                                                                    ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19346:45: note: previous declaration 'void (* __glewFragmentLightfSGIX)(GLenum, GLenum, GLfloat)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTFSGIXPROC __glewFragmentLightfSGIX;
                                             ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12325:93: error: 'void __glewFragmentLightfvSGIX(GLenum, GLenum, const GLfloat*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightfvSGIX (GLenum light, GLenum pname, const GLfloat *params);
                                                                                             ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19347:46: note: previous declaration 'void (* __glewFragmentLightfvSGIX)(GLenum, GLenum, GLfloat*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTFVSGIXPROC __glewFragmentLightfvSGIX;
                                              ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12326:82: error: 'void __glewFragmentLightiSGIX(GLenum, GLenum, GLint)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightiSGIX (GLenum light, GLenum pname, GLint param);
                                                                                  ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19348:45: note: previous declaration 'void (* __glewFragmentLightiSGIX)(GLenum, GLenum, GLint)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTISGIXPROC __glewFragmentLightiSGIX;
                                             ^~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12327:91: error: 'void __glewFragmentLightivSGIX(GLenum, GLenum, const GLint*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightivSGIX (GLenum light, GLenum pname, const GLint *params);
                                                                                           ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19349:46: note: previous declaration 'void (* __glewFragmentLightivSGIX)(GLenum, GLenum, GLint*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTIVSGIXPROC __glewFragmentLightivSGIX;
                                              ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12328:75: error: 'void __glewFragmentLightModelfSGIX(GLenum, GLfloat)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightModelfSGIX (GLenum pname, GLfloat param);
                                                                           ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19342:50: note: previous declaration 'void (* __glewFragmentLightModelfSGIX)(GLenum, GLfloat)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTMODELFSGIXPROC __glewFragmentLightModelfSGIX;
                                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12329:84: error: 'void __glewFragmentLightModelfvSGIX(GLenum, const GLfloat*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightModelfvSGIX (GLenum pname, const GLfloat *params);
                                                                                    ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19343:51: note: previous declaration 'void (* __glewFragmentLightModelfvSGIX)(GLenum, GLfloat*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTMODELFVSGIXPROC __glewFragmentLightModelfvSGIX;
                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12330:73: error: 'void __glewFragmentLightModeliSGIX(GLenum, GLint)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightModeliSGIX (GLenum pname, GLint param);
                                                                         ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19344:50: note: previous declaration 'void (* __glewFragmentLightModeliSGIX)(GLenum, GLint)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTMODELISGIXPROC __glewFragmentLightModeliSGIX;
                                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12331:82: error: 'void __glewFragmentLightModelivSGIX(GLenum, const GLint*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentLightModelivSGIX (GLenum pname, const GLint *params);
                                                                                  ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19345:51: note: previous declaration 'void (* __glewFragmentLightModelivSGIX)(GLenum, GLint*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTLIGHTMODELIVSGIXPROC __glewFragmentLightModelivSGIX;
                                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12332:86: error: 'void __glewFragmentMaterialfSGIX(GLenum, GLenum, GLfloat)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentMaterialfSGIX (GLenum face, GLenum pname, GLfloat param);
                                                                                      ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19350:48: note: previous declaration 'void (* __glewFragmentMaterialfSGIX)(GLenum, GLenum, GLfloat)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTMATERIALFSGIXPROC __glewFragmentMaterialfSGIX;
                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12333:95: error: 'void __glewFragmentMaterialfvSGIX(GLenum, GLenum, const GLfloat*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentMaterialfvSGIX (GLenum face, GLenum pname, const GLfloat *params);
                                                                                               ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19351:49: note: previous declaration 'void (* __glewFragmentMaterialfvSGIX)(GLenum, GLenum, const GLfloat*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTMATERIALFVSGIXPROC __glewFragmentMaterialfvSGIX;
                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12334:84: error: 'void __glewFragmentMaterialiSGIX(GLenum, GLenum, GLint)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentMaterialiSGIX (GLenum face, GLenum pname, GLint param);
                                                                                    ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19352:48: note: previous declaration 'void (* __glewFragmentMaterialiSGIX)(GLenum, GLenum, GLint)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTMATERIALISGIXPROC __glewFragmentMaterialiSGIX;
                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12335:93: error: 'void __glewFragmentMaterialivSGIX(GLenum, GLenum, const GLint*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glFragmentMaterialivSGIX (GLenum face, GLenum pname, const GLint *params);
                                                                                             ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19353:49: note: previous declaration 'void (* __glewFragmentMaterialivSGIX)(GLenum, GLenum, const GLint*)'
 GLEW_FUN_EXPORT PFNGLFRAGMENTMATERIALIVSGIXPROC __glewFragmentMaterialivSGIX;
                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12336:90: error: 'void __glewGetFragmentLightfvSGIX(GLenum, GLenum, GLfloat*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glGetFragmentLightfvSGIX (GLenum light, GLenum pname, GLfloat *params);
                                                                                          ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19354:49: note: previous declaration 'void (* __glewGetFragmentLightfvSGIX)(GLenum, GLenum, GLfloat*)'
 GLEW_FUN_EXPORT PFNGLGETFRAGMENTLIGHTFVSGIXPROC __glewGetFragmentLightfvSGIX;
                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12337:88: error: 'void __glewGetFragmentLightivSGIX(GLenum, GLenum, GLint*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glGetFragmentLightivSGIX (GLenum light, GLenum pname, GLint *params);
                                                                                        ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19355:49: note: previous declaration 'void (* __glewGetFragmentLightivSGIX)(GLenum, GLenum, GLint*)'
 GLEW_FUN_EXPORT PFNGLGETFRAGMENTLIGHTIVSGIXPROC __glewGetFragmentLightivSGIX;
                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12338:92: error: 'void __glewGetFragmentMaterialfvSGIX(GLenum, GLenum, GLfloat*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glGetFragmentMaterialfvSGIX (GLenum face, GLenum pname, GLfloat *params);
                                                                                            ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19356:52: note: previous declaration 'void (* __glewGetFragmentMaterialfvSGIX)(GLenum, GLenum, const GLfloat*)'
 GLEW_FUN_EXPORT PFNGLGETFRAGMENTMATERIALFVSGIXPROC __glewGetFragmentMaterialfvSGIX;
                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:212:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glext.h:12339:90: error: 'void __glewGetFragmentMaterialivSGIX(GLenum, GLenum, GLint*)' redeclared as different kind of symbol
 GLAPI void APIENTRY glGetFragmentMaterialivSGIX (GLenum face, GLenum pname, GLint *params);
                                                                                          ^
In file included from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofConstants.h:210:0,
                 from /home/user/of_v0.10.0_linux64gcc6_release/libs/openFrameworks/utils/ofSystemUtils.cpp:2:
/usr/include/GL/glew.h:19357:52: note: previous declaration 'void (* __glewGetFragmentMaterialivSGIX)(GLenum, GLenum, const GLint*)'
 GLEW_FUN_EXPORT PFNGLGETFRAGMENTMATERIALIVSGIXPROC __glewGetFragmentMaterialivSGIX;

DUH. My path variable was set up to use V0.10.0, not V0.11.0. Changed it and it worked.