Bug 805883: Add (void) cast to "use" an otherwise-unused variable, as far as GCC build-warning is concerned, in gc/Root.h. r=jorendorff

js/src/gc/Root.h

@@ -522,6 +522,7 @@ struct RootSink<JSStableString *> {
     static void dispose(JSStableString *ptr) {
         JSStableString * volatile sink;
         sink = ptr;
+        (void)sink; // silence GCC unused-but-set-variable build warning
     }
 };
 #endif