Enabling /ZW (CompileAsWinRT) option for msvs

test/win/compiler-flags/compile-as-winrt.cc

Index: test/win/compiler-flags/compile-as-winrt.cc
diff --git a/test/win/compiler-flags/compile-as-winrt.cc b/test/win/compiler-flags/compile-as-winrt.cc
new file mode 100644
index 0000000000000000000000000000000000000000..da9954f8fbce0af6962650fa1d636674db92e890
--- /dev/null
+++ b/test/win/compiler-flags/compile-as-winrt.cc
@@ -0,0 +1,12 @@
+// Copyright (c) 2016 Google Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+using namespace Platform;
+
+int main() {
+  wchar_t msg[] = L"Test";
+  String^ str1 = ref new String(msg);
+  auto str2 = String::Concat(str1, " Concat");
+  return 0;
+}