[builtins] Migrate Math.clz32 to a TurboFan builtin.

test/mjsunit/asm/math-clz32.js

 // Copyright 2015 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
-
 var stdlib = { Math: Math };
 
 var f = (function Module(stdlib) {
   "use asm";
 
   var clz32 = stdlib.Math.clz32;
 
   function f(a) {
     a = a >>> 0;
     return clz32(a)|0;
   }
 
   return f;
 })(stdlib);
 
 assertEquals(32, f(0));
 assertEquals(32, f(NaN));
 assertEquals(32, f(undefined));
 for (var i = 0; i < 32; ++i) {
   assertEquals(i, f((-1) >>> i));
 }
 for (var i = -2147483648; i < 2147483648; i += 3999773) {
-  assertEquals(%MathClz32(i), f(i));
-  assertEquals(%MathClz32(i), %_MathClz32(i >>> 0));
+  assertEquals(Math.clz32(i), f(i));
 }