Mac build fix. Macs don't support timeouts on locks.

Change-Id: I75665300d9b99420972865109026c8c090748cef
diff --git a/src/mutex.h b/src/mutex.h
index 4899382..edd458d 100644
--- a/src/mutex.h
+++ b/src/mutex.h
@@ -28,6 +28,13 @@
 #include "logging.h"
 #include "macros.h"
 
+// Currently Darwin doesn't support locks with timeouts.
+#if !defined(__APPLE__)
+#define HAVE_TIMED_RWLOCK 1
+#else
+#define HAVE_TIMED_RWLOCK 0
+#endif
+
 namespace art {
 
 class LOCKABLE Mutex;
@@ -271,7 +278,9 @@
 
   // Block until ReaderWriterMutex is free and acquire exclusive access. Returns true on success
   // or false if timeout is reached.
+#if HAVE_TIMED_RWLOCK
   bool ExclusiveLockWithTimeout(const timespec& abs_timeout) EXCLUSIVE_TRYLOCK_FUNCTION(true);
+#endif
 
   // Block until ReaderWriterMutex is shared or free then acquire a share on the access.
   void SharedLock() SHARED_LOCK_FUNCTION();