Add web compat workarounds for ES2015 RegExp semantics

test/webkit/fast/js/kde/RegExp-expected.txt

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 1.  Redistributions of source code must retain the above copyright
 #     notice, this list of conditions and the following disclaimer.
 # 2.  Redistributions in binary form must reproduce the above copyright
 #     notice, this list of conditions and the following disclaimer in the
@@ skipping 96 matching lines @@
 PASS reg.global === false is true
 PASS reg.multiline === false is true
 PASS reg.test('UGO') is true
 PASS reg.x = 1; reg.x is 1
 PASS var r2 = reg; r2.x = 2; reg.x is 2
 PASS str.match(re).toString() is 'Chapter 3.4.5.1,Chapter 3.4.5.1,.1'
 PASS str.match(/d/gi).toString() is 'D,d'
 PASS /\u0061/.source is '\\u0061'
 PASS 'abc'.match(/\u0062/).toString() is 'b'
 FAIL Object.prototype.toString.apply(RegExp.prototype) should be [object RegExp]. Was [object Object].
-FAIL typeof RegExp.prototype.toString() should be string. Threw exception TypeError: Method RegExp.prototype.toString called on incompatible receiver [object Object]
+PASS typeof RegExp.prototype.toString() is 'string'
 PASS new RegExp().toString() is '/(?:)/'
 PASS (new RegExp('(?:)')).source is '(?:)'
 PASS /(?:)/.toString() is '/(?:)/'
 PASS /(?:)/.source is '(?:)'
 Done.
 PASS successfullyParsed is true
 
 TEST COMPLETE