It is both evil and superfluous. It is evil because you should be writing portable code and do not depend on compiler specificities. It is superfluous because if you do not check, the compilation will still fail, which is precisely the expected behaviour.
> How exactly do you think simple, portable code is done?
By writing it carefully and testing it on different systems. You test with -Wall -Wextra -Werror -pedantic on all systems but you distribute the Makefile without these compiler flags.
> Do you expect code to compile on different platforms by magic?
No, of course. At first you will have a few linuxisms or macOS-isms, that you will gradually remove through a few rounds of multi-platform testing (which is free and easy to do nowadays).
