Fix compiler warnings about redefinition of GL_GLEXT_LEGACY
Fix compiler warnings about redefinition of GL_GLEXT_LEGACY

Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master