[crankshaft] do not sign-extend int32 immediate in DoMathMinMax.

test/mjsunit/regress/regress-crbug-495493.js

 // Copyright 2016 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: --harmony-explicit-tailcalls
-"use strict";
+// Flags: --nofold-constants --enable-slow-asserts --debug-code
 
-function f() {
-  return 1;
-}
-
-function g() {
-  for (var v in {a:0}) {
-    return continue f()  ;
+function foo(p) {
+  for (var i = 0; i < 100000; ++i) {
+    p = Math.min(-1, 0);
   }
 }
+foo(0);