Untested port of the SELinux dalvik change to art.

Change-Id: I26b473156fe965f6ee34d8cbca6719c71442d912
diff --git a/src/macros.h b/src/macros.h
index 28b9f7a..f7146ad 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -140,6 +140,8 @@
   _rc; })
 #endif
 
+template<typename T> void UNUSED(const T&) {}
+
 #if defined(__SUPPORT_TS_ANNOTATION__)
 
 #define ACQUIRED_AFTER(...) __attribute__ ((acquired_after(__VA_ARGS__)))