Tests/RunCMake/ObjectLibrary/requires.c - third_party/github.com/Kitware/CMake - Git at Google

 #ifdef REQUIRED
 int required(void)
 {
   return 0;
 }
 #else
 #  error "REQUIRED not defined"
 #endif
	#ifdef REQUIRED
	int required(void)
	{
	return 0;
	}
	#else
	# error "REQUIRED not defined"
	#endif