Revert of [regexp] Remove IsRegExp intrinsic

test/mjsunit/constant-fold-control-instructions.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: --allow-natives-syntax --fold-constants
 
 function test() {
   assertEquals("string", typeof "");
   assertEquals("number", typeof 1.1);
   assertEquals("number", typeof 1);
   assertEquals("boolean", typeof true);
   assertEquals("function", typeof function() {});
   assertEquals("object", typeof null);
   assertEquals("object", typeof {});
   assertEquals("object", typeof /regex/);
 
   assertTrue(%_IsSmi(1));
   assertFalse(%_IsSmi(1.1));
   assertFalse(%_IsSmi({}));
 
+  assertTrue(%_IsRegExp(/regexp/));
+  assertFalse(%_IsRegExp({}));
+
   assertTrue(%_IsArray([1]));
   assertFalse(%_IsArray(function() {}));
 
   assertTrue(%_IsJSReceiver(new Date()));
   assertFalse(%_IsJSReceiver(1));
 }
 
 
 test();
 test();
 %OptimizeFunctionOnNextCall(test);
 test();