Better implementation of should generate check: Only check stamps if the file is a uextern
Better implementation of should generate check: Only check stamps if the file is a uextern

Otherwise some other dependency might have changed. This has the benefit of bringing compilation down even more,
since we don't need to check timestamps all the time - macro times are now ~0.8s

proletariatgames/unreal.hx,proletariatgames/unreal.hx,proletariatgames/unreal.hx