[Bug libstdc++/128548] std::thread::join should check to make sure id is not __gthread_self before calling __gthread_join

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128548

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Glicb's pthread_join is documented to do the check and return EDEADLK, which is
probably why libstdc++ assumed that could be relied on. POSIX says it's
undefined though.