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_getpshared.c

@@ -28,6 +28,6 @@
  */
 errno_t pthread_condattr_getpshared(const pthread_condattr_t *attr,
                                     int *pshared) {
-  *pshared = *attr;
+  *pshared = attr->_pshared;
   return 0;
 }