Comment by pjmlp

You don't that is why people that never bothered with ISO C legalese have this idea of several tricks being C, when they are in practice "Their C Compiler" language.

Several things in C, if you want to stay within the guarantees of ISO C for portable code, have to be written in straight Assembly, not even inline, as the standard only defines a asm keyword must exist, leaving all other details to the implementation.