[turbofan] Fix invalid comparison operator narrowing.

test/mjsunit/regress/regress-v8-5254-2.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: --allow-natives-syntax
+
+var foo = (function() {
+  "use asm";
+  var a = new Uint8Array(2);
+  a[0] = 128;
+  a[1] = 127;
+
+  function foo() {
+    var x = a[0]|0;
+    var y = a[1]|0;
+    if (x < 0) x = 4294967296 + x|0;
+    if (y < 0) y = 4294967296 + y|0;
+    return x >= y;
+  }
+
+  return foo;
+})();
+
+assertTrue(foo());
+assertTrue(foo());
+%OptimizeFunctionOnNextCall(foo);
+assertTrue(foo());