[wasm][asm.js] Ensure final validation phase runs.

test/mjsunit/asm/regress-676573.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function baz() {
+  "use asm";
+}
+function B(stdlib, env) {
+  "use asm";
+  var x = env.foo | 0;
+}
+var bar = {
+  get foo() {
+  }
+};
+bar.__defineGetter__('foo', function() { return baz(); });
+B(this, bar);