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_init.c

@@ -24,6 +24,6 @@
  * @return 0 on success, or error on failure
  */
 errno_t pthread_condattr_init(pthread_condattr_t *attr) {
-  *attr = 0;
+  *attr = (pthread_condattr_t){0};
   return 0;
 }