[pthreads][condition variable] Added a pthreads unit test that uses condition variables
[pthreads][condition variable] Added a pthreads unit test that uses
condition variables

Uses only pthread_cond_wait() and pthread_cond_broadcast() for now.
pthread_cond_signal() does not work yet since it causes the futex
syscall to be called with the FUTEX_WAKE_OP operation which is not
documented in the manpages. None of the Splash2 benchmarks call the
futex syscall with the FUTEX_WAKE_OP operation.

8l/Graphite,mit-carbon/Graphite,mit-carbon/Graphite,fhijaz/Graphite,8l/Graphite,nkawahara/Graphite,8l/Graphite,fhijaz/Graphite,victorisildur/Graphite,nkawahara/Graphite,fhijaz/Graphite,victorisildur/Graphite,fhijaz/Graphite,victorisildur/Graphite,mit-carbon/Graphite,nkawahara/Graphite,victorisildur/Graphite,8l/Graphite,mit-carbon/Graphite,nkawahara/Graphite