Lithium: avoid registers for constants when possible.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index a978834c0ff9c855cb190d67be1ae05c50c2b179..ad95df4cac84728a7d067aaa1f732d76f5f5527d 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -1494,6 +1494,7 @@ HInstruction* HGraphBuilder::BuildStoreMap(HValue* object,
   HInstruction* store_map =
       new(zone) HStoreNamedField(object, map_field_name, map,
                                  true, JSObject::kMapOffset);
+  store_map->ClearGVNFlag(kChangesInobjectFields);
   store_map->SetGVNFlag(kChangesMaps);
   AddInstruction(store_map);
   return store_map;