Add fatal error in CMake when trying to build WITH_GAMEENGINE but without WITH_LEGACY_OPENGL

This won't work currently.

CMakeLists.txt

@@ -681,6 +681,10 @@ if(NOT WITH_GAMEENGINE AND WITH_PLAYER)
 	message(FATAL_ERROR "WITH_PLAYER requires WITH_GAMEENGINE")
 endif()
 
+if(WITH_GAMEENGINE AND NOT WITH_LEGACY_OPENGL)
+	message(FATAL_ERROR "WITH_GAME_ENGINE requires WITH_LEGACY_OPENGL")
+endif()
+
 if(NOT WITH_AUDASPACE)
 	if(WITH_OPENAL)
 		message(FATAL_ERROR "WITH_OPENAL requires WITH_AUDASPACE")