[CMake] Add OpenGL as requiered dependency for OSX

CMakeLists.txt

@@ -62,6 +62,11 @@ add_definitions(
   -DPYTHONQT_SUPPORT_NAME_PROPERTY
   )
 
+#-----------------------------------------------------------------------------
+# OpenGL libraries
+
+find_package(OpenGL REQUIRED)
+
 #-----------------------------------------------------------------------------
 # Build options
 
@@ -343,6 +348,7 @@ add_library(PythonQt SHARED
             ${sources}
             ${gen_moc_sources}
   )
+target_link_libraries(PythonQt ${OPENGL_LIBRARY})
 set_target_properties(PythonQt PROPERTIES DEFINE_SYMBOL PYTHONQT_EXPORTS)
 
 target_link_libraries(PythonQt