Use relative path to cygwin on Windows for the runtime

bin/bin.gypi

 # 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': {
     'builtin_in_cc_file': 'builtin_in.cc',
     'builtin_cc_file': '<(SHARED_INTERMEDIATE_DIR)/builtin_gen.cc',
     'snapshot_in_cc_file': 'snapshot_in.cc',
     'snapshot_bin_file': '<(SHARED_INTERMEDIATE_DIR)/snapshot_gen.bin',
     'snapshot_cc_file': '<(SHARED_INTERMEDIATE_DIR)/snapshot_gen.cc',
+    'cygwin_dir': '../../third_party/cygwin',
   },
   'targets': [
     {
       'target_name': 'generate_builtin_cc_file',
       'type': 'none',
       'conditions': [
         ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(DEPTH)/third_party/cygwin'],
+          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
         }],
       ],
       'sources': [
         'builtin.dart',
         'buffer_list.dart',
         'directory.dart',
         'directory_impl.dart',
         'eventhandler.dart',
         'file.dart',
         'file_impl.dart',
@@ skipping 134 matching lines @@
             'libraries': [ '-lws2_32.lib', '-lRpcrt4.lib' ],
           },
        }]],
     },
     {
       # Generate snapshot file.
       'target_name': 'generate_snapshot_file',
       'type': 'none',
       'conditions': [
         ['OS=="win"', {
-          'msvs_cygwin_dirs': ['<(DEPTH)/third_party/cygwin'],
+          'msvs_cygwin_dirs': ['<(cygwin_dir)'],
         }],
       ],
       'dependencies': [
         'gen_snapshot_bin',
       ],
       'actions': [
         {
           'action_name': 'generate_snapshot_file',
           'inputs': [
             '../tools/create_snapshot_file.py',
@@ skipping 183 matching lines @@
         ]}],
         ['OS=="win"', {
           'link_settings': {
             'libraries': [ '-lws2_32.lib', '-lRpcrt4.lib' ],
           },
         }],
       ],
     },
   ],
 }