Suppress loading site packages when running gyp from tools/gyp_dart.py.

tools/gyp_dart.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 The Dart Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Invoke gyp to generate build files for building the Dart VM.
 """
 
 import os
 import subprocess
 import sys
 
 def execute(args):
   process = subprocess.Popen(args)
   process.wait()
   return process.returncode
 
 def main():
   component = 'all'
   if len(sys.argv) == 2:
     component = sys.argv[1]
 
   component_gyp_files = {
     'all' : 'dart/dart.gyp',
     'runtime' : 'dart/runtime/dart-runtime.gyp',
   }
-  args = ['python', 'dart/third_party/gyp/gyp_main.py',
+  args = ['python', '-S', 'dart/third_party/gyp/gyp_main.py',
           '--depth=dart', '-Idart/tools/gyp/all.gypi',
           component_gyp_files[component]]
 
   if sys.platform == 'win32':
     # Generate Visual Studio 2010 compatible files by default.
     if not os.environ.get('GYP_MSVS_VERSION'):
       args.extend(['-G', 'msvs_version=2010'])
 
   sys.exit(execute(args))
 
 if __name__ == '__main__':
   main()