> "-fno-math-errno" ... can be turned on without any problems. There is even a good reason for that, math-errno is a posix requirement and completely optional

> "-fno-math-errno" ... can be turned on without any problems. There is even a good reason for that, math-errno is a posix requirement and completely optional in both C and C++ standards. If your code is intended to be portable it should avoid relying on this anti-feature anyway.