Fix mac gyp generation by moving target to seperate file.

pkg/pkg_files.gyp

+# Copyright (c) 2014, 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.
+
+{
+  'targets': [
+    # Other targets depend on pkg files, but have to many inputs, which causes
+    # issues on some platforms.
+    # This target lists all the files in pkg and third_party/pkg,
+    # and creates a single pkg_files.stamp
+    {
+      'target_name': 'pkg_files_stamp',
+      'type': 'none',
+      'actions': [
+        {
+          'action_name': 'make_pkg_files_stamp',
+          'inputs': [
+            '../tools/create_timestamp_file.py',
+            '<!@(["python", "../tools/list_files.py", "", "."])',
+            '<!@(["python", "../tools/list_files.py", "",'
+                '"../third_party/pkg"])',
+          ],
+          'outputs': [
+            '<(SHARED_INTERMEDIATE_DIR)/pkg_files.stamp',
+          ],
+          'action': [
+            'python', '../tools/create_timestamp_file.py',
+            '<@(_outputs)',
+          ],
+        },
+      ],
+    }
+  ],
+}