Make built-ins strict mode conforming, and support a --use-strict flag.

test/mjsunit/builtins.js

 // Copyright 2011 the V8 project authors. All rights reserved.
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 // Flags: --expose-natives-as=builtins
 
-// Checks that all function properties of the builtin object are neither
-// writable nor configurable. Also, theose functions that are actually
+// Checks that all function properties of the builtin object that are actually
 // constructors (recognized by having properties on their .prototype object),
 // have only unconfigurable properties on the prototype, and the methods
 // are also non-writable.
 
 var names = Object.getOwnPropertyNames(builtins);
 
 function isFunction(obj) {
   return typeof obj == "function";
 }
 
@@ skipping 26 matching lines @@
     }
   }
 }
 
 for (var i = 0; i < names.length; i++) {
   var name = names[i];
   var desc = Object.getOwnPropertyDescriptor(builtins, name);
   assertTrue(desc.hasOwnProperty("value"));
   var value = desc.value;
   if (isFunction(value)) {
-    assertFalse(desc.writable, name);
-    assertFalse(desc.configurable, name);
     checkConstructor(value, name);
   }
 }