Revert "Quick compiler: disable GVN DO NOT MERGE"

This reverts commit 4c4f4daafbac15b856da91118d9ea55c9eefa54b.
diff --git a/compiler/dex/frontend.cc b/compiler/dex/frontend.cc
index e93827d..07f3033 100644
--- a/compiler/dex/frontend.cc
+++ b/compiler/dex/frontend.cc
@@ -40,7 +40,7 @@
   // (1 << kSuppressLoads) |
   // (1 << kNullCheckElimination) |
   // (1 << kClassInitCheckElimination) |
-  (1 << kGlobalValueNumbering) |
+  // (1 << kGlobalValueNumbering) |
   // (1 << kPromoteRegs) |
   // (1 << kTrackLiveTemps) |
   // (1 << kSafeOptimizations) |