Move cygwin_dir to common.gypi.

dart/tools/gyp/all.gypi

Index: dart/tools/gyp/all.gypi
diff --git a/dart/tools/gyp/all.gypi b/dart/tools/gyp/all.gypi
index 63e9e75379a483ab17c5b5fee67e2e62f1c2612d..23d9f86a2d851ef1f6569d7cb9785ec42342d0a8 100644
--- a/dart/tools/gyp/all.gypi
+++ b/dart/tools/gyp/all.gypi
@@ -1,4 +1,4 @@
-# Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+# Copyright (c) 2012, 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.
 
@@ -19,6 +19,11 @@
         'ldflags': [ '-pthread', ],
       },
     }],
+    [ 'OS=="win"', {
+      'target_defaults': {
+        'msvs_cygwin_dirs': ['<(DEPTH)/third_party/cygwin'],
+      },
+    }],
   ],
   'includes': [
     'xcode.gypi',