[Bug preprocessor/80753] __has_include and __has_include_next taints subsequent I/O errors

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80753

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This means the following paradox compiles OK:

#if ! __has_include(<nonesuch>)
# include <nonesuch>
#endif