Implement POSIX pthread_mutex_timedlock.

This replaces the non-standard pthread_mutex_lock_timeout_np, which we have
to keep around on LP32 for binary compatibility.

Change-Id: I098dc7cd38369f0c1bec1fac35687fbd27392e00

libc/bionic/pthread_cond.cpp

@@ -185,7 +185,7 @@ int __pthread_cond_timedwait(pthread_cond_t* cond, pthread_mutex_t* mutex, const
   timespec* tsp;
 
   if (abstime != NULL) {
-    if (__timespec_to_absolute(&ts, abstime, clock) < 0) {
+    if (__timespec_from_absolute(&ts, abstime, clock) < 0) {
       return ETIMEDOUT;
     }
     tsp = &ts;