https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119753
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- POSIX is talking about the 'c17' utility, not a command called 'gcc'. I don't think GCC claims to be equivalent to 'c17'. Any 'c99' or 'c17' utility you have is not part of upstream GCC but is installed by your distro. A new option or environment variable that makes 'gcc' more compatible with the POSIX requirements does seem reasonable though.
