Add boolean flag to HChange and LNumberUntagD to not convert undefined to NaN.

test/mjsunit/regress/regress-1434.js

-// Copyright 2008 the V8 project authors. All rights reserved.
+// Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
@@ skipping 15 matching lines @@
 
 // Flags: --allow-natives-syntax
 
 function compare(a, b) {
   return a === b;
 }
 
 compare(1.5, 2.5);
 %OptimizeFunctionOnNextCall(compare);
 assertTrue(compare(undefined, undefined));