Tests/SetLang/stay_cxx.cxx - third_party/github.com/Kitware/CMake - Git at Google

 #ifndef __cplusplus
 #  error C++ source incorrectly compiled as C
 #endif

 int stay_cxx()
 {
   return 0;
 }
	#ifndef __cplusplus
	# error C++ source incorrectly compiled as C
	#endif

	int stay_cxx()
	{
	return 0;
	}