Fix windows build create_sdk.

dart.gyp

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     # These variables are used in the creation of the .vcproj file on 
     # Windows.
     'cygwin_dir': 'third_party/cygwin',
-    'msvs_cygwin_dirs': ['<(cygwin_dir)'],
   },
   'targets': [
     {
       'target_name': 'compiler',
       'type': 'none',
       'dependencies': [
         'compiler/dart-compiler.gyp:dartc',
       ],
       'actions': []
     },
@@ skipping 16 matching lines @@
     {
       'target_name': 'frogsh',
       'type': 'none',
       'dependencies': [
         'frog/dart-frog.gyp:frogsh',
       ],
     },
     {
       'target_name': 'create_sdk',
       'type': 'none',
+      'conditions': [
+        ['OS=="win"', {
+          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
+        }],
+      ],
       'dependencies': [
         'frog',
         'runtime',
       ],
       'actions': [
         {
           'action_name': 'create_sdk_py',
           'inputs': [
             # TODO(dgrove) - change these to dependencies and add dom
             # dependences once issues 754 and 755 are fixed
@@ skipping 45 matching lines @@
     # so don't build it for now.
     #{
     #  'target_name': 'client',
     #  'type': 'none',
     #  'dependencies': [
     #    'client/dart.gyp:fling',
     #  ],
     #},
   ],
 }