Fix mint shifting by zero on MIPS (issue 23117).

tests/language/vm/regress_23117_vm_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+// Test location summary for Uint32 multiplication.
+// VMOptions=--optimization-counter-threshold=5
+
+import 'package:expect/expect.dart';
+
+mintLeftShift(x, y) => x << y;
+mintRightShift(x, y) => x >> y;
+
+main() {
+  for (var i = 0; i < 20; i++) {
+    var x = 1 + (1 << (i + 32));
+    Expect.equals(x, mintLeftShift(x, 0));
+    Expect.equals(x, mintRightShift(x, 0));
+    Expect.equals(2*x, mintLeftShift(x, 1));
+    Expect.equals(x~/2, mintRightShift(x, 1));
+    Expect.equals(x, mintRightShift(mintLeftShift(x, i), i));
+  }
+}