GL_EXT_x11_sync_object
http://www.opengl.org/registry/specs/gl/EXT/x11_sync_object.txt
GL_EXT_x11_sync_object
	GL_SYNC_X11_FENCE_EXT 0x90E1
	GLsync glImportSyncEXT (GLenum external_sync_type, GLintptr external_sync, GLbitfield flags)