ART: Add -Wunused

Until the global CFLAGS are fixed, add Wunused. Fix declarations
in the optimizing compiler.

Change-Id: Ic4553f08e809dc54f3d82af57ac592622c98e000
diff --git a/compiler/optimizing/licm.h b/compiler/optimizing/licm.h
index 4812394..cb6170e 100644
--- a/compiler/optimizing/licm.h
+++ b/compiler/optimizing/licm.h
@@ -31,6 +31,8 @@
 
   void Run() OVERRIDE;
 
+  static constexpr const char* kLoopInvariantCodeMotionPassName = "licm";
+
  private:
   const SideEffectsAnalysis& side_effects_;