clang packager/win: Check that GnuWin32 is in the path at the start.

tools/clang/scripts/package.py

 #!/usr/bin/env python
 # Copyright (c) 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """This script will check out llvm and clang, and then package the results up
 to a tgz file."""
 
 import argparse
 import fnmatch
@@ skipping 40 matching lines @@
     print 'Failed:', cmd
     sys.exit(1)
 
 
 def PrintTarProgress(tarinfo):
   print 'Adding', tarinfo.name
   return tarinfo
 
 
 def main():
+  if sys.platform == 'win32':
+    try:
+      subprocess.check_output(['grep', '--help'], shell=True)
+    except subprocess.CalledProcessError:
+      print 'Add gnuwin32 to your PATH, then try again.'
+      return 1
+
   parser = argparse.ArgumentParser(description='build and package clang')
   parser.add_argument('--gcc-toolchain',
                       help="the prefix for the GCC version used for building. "
                            "For /opt/foo/bin/gcc, pass "
                            "'--gcc-toolchain '/opt/foo'")
 
   args = parser.parse_args()
 
   with open('buildlog.txt', 'w') as log:
     Tee('Diff in llvm:\n', log)
@@ skipping 158 matching lines @@
               filter=PrintTarProgress)
     print ('gsutil cp -a public-read %s.tgz '
            'gs://chromium-browser-clang/%s/%s.tgz') % (golddir, platform,
                                                        golddir)
 
   # FIXME: Warn if the file already exists on the server.
 
 
 if __name__ == '__main__':
   sys.exit(main())