avoid find_package(OpenGL) that requires GLX
check glu because that's what xmoto uses
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -39,7 +39,7 @@ find_package(LibLZMA)
 find_package(LibXml2 REQUIRED)
 
 if(USE_OPENGL)
-  find_package(OpenGL REQUIRED)
+  pkg_check_modules(OPENGL glu REQUIRED)
 endif()
 
 if(APPLE)