Now we have a proper C++ library, use std::unique_ptr.

Also remove the Android.libcxx.mk and other bits of stlport compatibility
mechanics.

Change-Id: Icdf7188ba3c79cdf5617672c1cfd0a68ae596a61
diff --git a/runtime/barrier.h b/runtime/barrier.h
index d3e6bae..a433cac 100644
--- a/runtime/barrier.h
+++ b/runtime/barrier.h
@@ -17,8 +17,8 @@
 #ifndef ART_RUNTIME_BARRIER_H_
 #define ART_RUNTIME_BARRIER_H_
 
+#include <memory>
 #include "base/mutex.h"
-#include "UniquePtrCompat.h"
 
 namespace art {