Avoid -O3 in nacl as it does not play well with -W.

src/effects.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 37 matching lines @@
 // effect cancels out any previous effect upon sequencing. A possible effect
 // merges into a previous effect, i.e., type bounds are merged. Alternative
 // composition always merges bounds. It yields a possible effect if at least
 // one was only possible.
 struct Effect {
   enum Modality { POSSIBLE, DEFINITE };
 
   Modality modality;
   Bounds bounds;
 
-  Effect() {}
+  Effect() : modality(DEFINITE) {}
   Effect(Bounds b, Modality m = DEFINITE) : modality(m), bounds(b) {}
 
   // The unknown effect.
   static Effect Unknown(Isolate* isolate) {
     return Effect(Bounds::Unbounded(isolate), POSSIBLE);
   }
 
   static Effect Forget(Isolate* isolate) {
     return Effect(Bounds::Unbounded(isolate), DEFINITE);
   }
@@ skipping 283 matching lines @@
     NestedEffects result = *this;
     result.pop();
     ASSERT(!this->is_empty());
     return result;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_EFFECTS_H_