[Bug preprocessor/80005] cpp expands __has_include() filename parts

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80005

--- Comment #9 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
Florian, the trouble is the older glibcs are out there and people's code will
immediately break.  That would be bad.