ninja windows: support precompiled headers

test/msvs/precompiled/hello2.c

Index: test/msvs/precompiled/hello2.c
diff --git a/test/msvs/precompiled/hello2.c b/test/msvs/precompiled/hello2.c
deleted file mode 100644
index d6d53111fb80d5163769ba7a612ee25806ba90ba..0000000000000000000000000000000000000000
--- a/test/msvs/precompiled/hello2.c
+++ /dev/null
@@ -1,13 +0,0 @@
-/* Copyright (c) 2011 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. */
-
-// Unlike hello.c, this file specifies the headers.
-
-#include <windows.h>
-#include <stdio.h>
-
-int hello2() {
-  printf("Hello, two!\n");
-  return 0;
-}