In OptionsGTK.cmake we have this: # This part can be simplified once CMake 2.8.6 is required and # CMakePushCheckState can be used. We need to have OPENGL_INCLUDE_DIR as part # of the directories check_include_files() looks for in case OpenGL is # installed into a non-standard location. if (ENABLE_X11_TARGET) set(REQUIRED_INCLUDES_OLD ${CMAKE_REQUIRED_INCLUDES}) set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${OPENGL_INCLUDE_DIR}) set(CMAKE_REQUIRED_INCLUDES ${REQUIRED_INCLUDES_OLD}) ... endif () Which does nothing. This broke sometime recentlyish when the check for GLX moved elsewhere in the file. Should be: set(REQUIRED_INCLUDES_OLD ${CMAKE_REQUIRED_INCLUDES}) set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${OPENGL_INCLUDE_DIR}) # We don't use find_package for GLX because it is part of -lGL, unlike EGL. check_include_files("GL/glx.h" GLX_FOUND) set(CMAKE_REQUIRED_INCLUDES ${REQUIRED_INCLUDES_OLD}) I will fix this in bug #143558, since it is hard to split my changes to OptionsGTK.cmake into multiple patches. I'm filing this bug just to make sure we don't lose track of it.
Note that we nowadays require CMake 2.8.8.