Introduce pthread_rwlock_try{rd,wr}lock

This also changes recursive mutexes to favor cpu over scheduler yield.

libc/intrin/pthread_mutex_unlock.c

@@ -34,7 +34,7 @@
  * @raises EPERM if in error check mode and not owned by caller
  * @vforksafe
  */
-int pthread_mutex_unlock(pthread_mutex_t *mutex) {
+errno_t pthread_mutex_unlock(pthread_mutex_t *mutex) {
   int t;
 
   LOCKTRACE("pthread_mutex_unlock(%t)", mutex);