Add an option to prune unwanted targets

test/prune_targets/test1.gyp

Index: test/prune_targets/test1.gyp
diff --git a/test/win/generator-output-different-drive/prog.gyp b/test/prune_targets/test1.gyp
similarity index 58%
copy from test/win/generator-output-different-drive/prog.gyp
copy to test/prune_targets/test1.gyp
index 92f53e5da56f441abd6471673ae0ce597aa8f5dc..81b46846f3023e4a0f8bf71ae153f67d510b9f89 100644
--- a/test/win/generator-output-different-drive/prog.gyp
+++ b/test/prune_targets/test1.gyp
@@ -1,4 +1,4 @@
-# Copyright 2013 The Chromium Authors. 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.
 
@@ -7,9 +7,8 @@
     {
       'target_name': 'program',
       'type': 'executable',
-      'sources': [
-        'prog.c',
-      ],
+      'sources': [ 'program.cc' ],
+      'dependencies': [ 'test2.gyp:lib_wanted' ],
     },
   ],
 }