Move mutex, condvar, and thread-specific data routes, pthread_once, and
pthread_exit from libpthread to libc, along with low-level bits to
support them. Major bump to both libc and libpthread.

Requ

Move mutex, condvar, and thread-specific data routes, pthread_once, and
pthread_exit from libpthread to libc, along with low-level bits to
support them. Major bump to both libc and libpthread.

Requested by libressl team. Ports testing by naddy@
ok kettenis@

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