Tests/TryCompile/testdef.c - third_party/github.com/Kitware/CMake - Git at Google

 #ifndef TESTDEF
 #  error "TESTDEF should be defined!"
 #endif
 int main(void)
 {
   return 0;
 }
	#ifndef TESTDEF
	# error "TESTDEF should be defined!"
	#endif
	int main(void)
	{
	return 0;
	}