Introduce a BuiltinsConstructStub that sets up new.target and does a [[call]] per ES6 9.3.2

test/webkit/regexp-compile.js

 // 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 37 matching lines @@
 
 shouldThrow("re.compile(new RegExp('c'), 'i');");
 
 // It's OK to supply a second argument, as long as the argument is "undefined".
 re.compile(re, undefined);
 shouldBe("re.toString()", "'/c/i'");
 
 shouldThrow("re.compile(new RegExp('+'));");
 
 re.compile(undefined);
-shouldBe("re.toString()", "'/undefined/'");
+shouldBe("re.toString()", "'/(?:)/'");
 
 re.compile(null);
 shouldBe("re.toString()", "'/null/'");
 
 re.compile();
 shouldBe("re.toString()", "'/(?:)/'");
 
 re.compile("z", undefined);
 shouldBe("re.toString()", "'/z/'");
 
 // Compiling should reset lastIndex.
 re.lastIndex = 100;
 re.compile(/a/g);
 shouldBe("re.lastIndex", "0");
 re.exec("aaa");
 shouldBe("re.lastIndex", "1");