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/ssa_phi_elimination.h b/compiler/optimizing/ssa_phi_elimination.h
index 88a5279..c4b63ab 100644
--- a/compiler/optimizing/ssa_phi_elimination.h
+++ b/compiler/optimizing/ssa_phi_elimination.h
@@ -29,7 +29,7 @@
 class SsaDeadPhiElimination : public HOptimization {
  public:
   explicit SsaDeadPhiElimination(HGraph* graph)
-      : HOptimization(graph, true, "dead_phi_elimination"),
+      : HOptimization(graph, true, kSsaDeadPhiEliminationPassName),
         worklist_(graph->GetArena(), kDefaultWorklistSize) {}
 
   void Run() OVERRIDE;
@@ -37,6 +37,8 @@
   void MarkDeadPhis();
   void EliminateDeadPhis();
 
+  static constexpr const char* kSsaDeadPhiEliminationPassName = "dead_phi_elimination";
+
  private:
   GrowableArray<HPhi*> worklist_;
 
@@ -54,11 +56,13 @@
 class SsaRedundantPhiElimination : public HOptimization {
  public:
   explicit SsaRedundantPhiElimination(HGraph* graph)
-      : HOptimization(graph, true, "redundant_phi_elimination"),
+      : HOptimization(graph, true, kSsaRedundantPhiEliminationPassName),
         worklist_(graph->GetArena(), kDefaultWorklistSize) {}
 
   void Run() OVERRIDE;
 
+  static constexpr const char* kSsaRedundantPhiEliminationPassName = "redundant_phi_elimination";
+
  private:
   GrowableArray<HPhi*> worklist_;