Fix precompiled header test

test/msvs/precompiled/hello.gyp

-# Copyright (c) 2011 Google Inc. All rights reserved.
+# Copyright (c) 2012 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.
 
 {
   'targets': [
     {
       'target_name': 'hello',
       'type': 'executable',
       'sources': [
         'hello.c',
         'hello2.c',
         'precomp.c',
       ],
       'msvs_precompiled_header': 'stdio.h',
       'msvs_precompiled_source': 'precomp.c',
+
+      # Required so that the printf actually causes a build failure
+      # if the pch isn't included.
+      'msvs_settings': {
+        'VCCLCompilerTool': {
+          'WarningLevel': '3',
+          'WarnAsError': 'true',
+        },
+      },
     },
   ],
 }