Fix overflow check when shifting unboxed mints on 32-bit platforms, except on

tests/corelib/regress_r21715_test.dart

+// Copyright (c) 2014, 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.
+
+// VMOptions=--optimization_counter_threshold=5
+
+import "package:expect/expect.dart";
+
+sll(x, shift) => x << shift;
+
+main() {
+  for (int i = 0; i < 10; i++) {
+    var x = 0x50000000;
+    var shift = 34;
+    Expect.equals(sll(x, shift), 0x14000000000000000);
+  }
+}