[Bug libstdc++/57740] C++11 std::thread not usable with static linking

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57740

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Since r213922 pthread_create should get linked in, but apparently not
pthread_join.