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/builder.h b/compiler/optimizing/builder.h
index 3e4a616..96196de 100644
--- a/compiler/optimizing/builder.h
+++ b/compiler/optimizing/builder.h
@@ -80,6 +80,8 @@
 
   bool BuildGraph(const DexFile::CodeItem& code);
 
+  static constexpr const char* kBuilderPassName = "builder";
+
  private:
   // Analyzes the dex instruction and adds HInstruction to the graph
   // to execute that instruction. Returns whether the instruction can