ART: More warnings

Enable -Wno-conversion-null, -Wredundant-decls and -Wshadow in general,
and -Wunused-but-set-parameter for GCC builds.

Change-Id: I81bbdd762213444673c65d85edae594a523836e5
diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc
index a0cc8a9..e83c528 100644
--- a/compiler/optimizing/ssa_builder.cc
+++ b/compiler/optimizing/ssa_builder.cc
@@ -109,8 +109,8 @@
         HPhi* phi = new (GetGraph()->GetArena()) HPhi(
             GetGraph()->GetArena(), local, block->GetPredecessors().Size(), Primitive::kPrimVoid);
         for (size_t i = 0; i < block->GetPredecessors().Size(); i++) {
-          HInstruction* value = ValueOfLocal(block->GetPredecessors().Get(i), local);
-          phi->SetRawInputAt(i, value);
+          HInstruction* pred_value = ValueOfLocal(block->GetPredecessors().Get(i), local);
+          phi->SetRawInputAt(i, pred_value);
         }
         block->AddPhi(phi);
         value = phi;