Fix bug with re-scoping arrow function parameter initializers

test/mjsunit/regress/regress-622663.js

++// Copyright 2016 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: --ignition --no-lazy

[rmcilroy, 2016/06/24 14:34:00]

Maybe don't set the --ignition flag -  we have a variant which runs all tests
with the --ignition flag, so there will be better test coverage without
explicitly adding this flag (will test both FCG and Ignition)

[nickie, 2016/06/24 14:36:55]

Acknowledged.

+
+(function() {
+  try { (y = [...[]]) => {} } catch(_) {}  // will core dump, if not fixed
+})();