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@
it's now atomic_lock to better reflect its usage, and librthread now
features a new spinlock that's really a ticket lock.
thrlseep can handle both types of lock via a flag in the clock arg.
(temp back compat hack)
remove some old stuff that's accumulated along the way and no longer used.
some feedback from dlg, who is concerned with all things ticket lock.
(you need to boot a new kernel before installing librthread)
