First crack at adding a GYP_GENERATOR for determining various things

test/analyzer/subdir/subdir.gyp

 # Copyright (c) 2014 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.
 
 {
+  'variables': {
+    'trailing_dir_path': '../',
+   },
   'targets': [
     {
-      'target_name': 'hello',
-      'type': 'executable',
+      'target_name': 'foo',
+      'type': 'static_library',
       'sources': [
-        'hello.c',
+        'subdir_source.c',
+        '<(trailing_dir_path)/parent_source.c',
       ],
     },
   ],
 }