pthread_cond_timedwait() is called before any threads have been
created and the SA infrastructure is up and running.
Addresses PR lib/20139.
XXX probably need to do this for all of the pthread_*_timedlock()
functions, too.
pthread_cond_broadcast(): use double-checked locking to avoid
pthread__self() and pthread_spinlock() when signaling or broadcasting
on a condition variable with no waiters.
lukem