Fix desugaring of let bindings in for loops to handle continue properly

test/mjsunit/harmony/regress/regress-3683.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: --harmony-scoping
+
+"use strict";
+
+var count = 0;
+for (let x = 0; x < 10;) {
+  x++;
+  count++;
+  continue;
+}
+assertEquals(10, count);
+
+count = 0;
+label: for (let x = 0; x < 10;) {
+  while (true) {
+    x++;
+    count++;
+    continue label;
+  }
+}
+assertEquals(10, count);
+
+count = 0;
+for (let x = 0; x < 10;) {
+  x++;
+  count++;
+  {
+    let x = "hello";
+    continue;
+  }
+}
+assertEquals(10, count);