Introduce pthread_condattr_setclock()

This is one of the few POSIX APIs that was missing. It lets you choose a
monotonic clock for your condition variables. This might improve perf on
some platforms. It might also grant more flexibility with NTP configs. I
know Qt is one project that believes it needs this. To introduce this, I
needed to change some the *NSYNC APIs, to support passing a clock param.
There's also new benchmarks, demonstrating Cosmopolitan's supremacy over
many libc implementations when it comes to mutex performance. Cygwin has
an alarmingly bad pthread_mutex_t implementation. It is so bad that they
would have been significantly better off if they'd used naive spinlocks.

libc/thread/pthread_condattr_setpshared.c

@@ -32,7 +32,7 @@ errno_t pthread_condattr_setpshared(pthread_condattr_t *attr, int pshared) {
   switch (pshared) {
     case PTHREAD_PROCESS_SHARED:
     case PTHREAD_PROCESS_PRIVATE:
-      *attr = pshared;
+      attr->_pshared = pshared;
       return 0;
     default:
       return EINVAL;