On Windows, don't try to create relative paths across different drives

test/win/generator-output-different-drive/prog.gyp

Index: test/win/generator-output-different-drive/prog.gyp
===================================================================
--- test/win/generator-output-different-drive/prog.gyp	(revision 0)
+++ test/win/generator-output-different-drive/prog.gyp	(working copy)
@@ -1,14 +1,14 @@
-# Copyright (c) 2009 Google Inc. All rights reserved.
+# Copyright (c) 2013 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': 'program1',
+      'target_name': 'program',
       'type': 'executable',
       'sources': [
-        'prog1.c',
+        'prog.c',
       ],
     },
   ],