Ship ES2015 sloppy-mode const semantics

test/mjsunit/regress/regress-3138.js

 // Copyright 2014 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.
 
+// Flags: --legacy-const
+
 (function f(){
    assertEquals("function", typeof f);
 })();
 
 (function f(){
    var f;  // Variable shadows function name.
    assertEquals("undefined", typeof f);
 })();
 
 (function f(){
@@ skipping 16 matching lines @@
 
 // const initialization is not intercepted by with scope.
 (function() {
   var o = { a: 1 };
   with (o) {
     const a = 2;
   }
   assertEquals(2, a);
   assertEquals(1, o.a);
 })();