[Bug libstdc++/60645] locale::facet::_S_get_c_locale does not handle __gthread_once error codes.

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60645

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The only error code specified by POSIX is EINVAL which cannot happen here,
because the pthread_once_t is statically initialized and controlled entirely by
the library.