link pthread_join from std::thread ctor

link pthread_join from std::thread ctor

Like pthread_create, pthread_join may fail to be statically linked in
absent strong uses, so add to user code strong references to both when
std::thread objects are created.

for  libstdc++-v3/ChangeLog

	PR libstdc++/104852
	PR libstdc++/95989
	PR libstdc++/52590
	* include/bits/std_thread.h (thread::_M_thread_deps): New
	static implicitly-inline member function.
	(std::thread template ctor): Pass it to _M_start_thread.
	* src/c++11/thread.cc (thread::_M_start_thread): Name depend
	parameter, force it live on entry.