[Bug libgcc/65281] Lots of macros using non-reserved names in gthr headers

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65281

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC_GTHR_POSIX_H gets converted into _GLIBCXX_GCC_GTHR_POSIX_H

I think UNUSED was GCC_GTHR_UNUSED it would have been converted into
_GLIBCXX_GCC_GTHR_UNUSED