Linux: Fix __glibc_has_include use for <sys/stat.h> and statx

The identifier linux is used as a predefined macro, so the actually
used path is 1/stat.h or 1/stat64.h.  Using the quote-based version
triggers a file lookup for /usr/include/bits/linux/stat.h (or whatever
directory is used to store bits/statx.h), but since bits/ is pretty
much reserved by glibc, this appears to be acceptable.

This is related to GCC PR 80005: incorrect macro expansion of the
argument of __has_include.

Suggested by Zack Weinberg.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>