Tests/RunCMake/try_compile/src.c - third_party/github.com/Kitware/CMake - Git at Google

 int main(void)
 {
   return 0;
 }
 #ifdef PP_ERROR
 #  error PP_ERROR is defined
 #endif
	int main(void)
	{
	return 0;
	}
	#ifdef PP_ERROR
	# error PP_ERROR is defined
	#endif