Update Clang update.py for the 3.9.0 version bump

tools/clang/scripts/update.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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 is used to download prebuilt clang binaries.
 
 It is also used by package.py to build the prebuilt clang binaries."""
 
 import argparse
@@ skipping 769 matching lines @@
     # clang previously downloaded, keep it up-to-date.
     # If you don't want this, delete third_party/llvm-build on your machine.
     if os.path.isdir(LLVM_BUILD_DIR):
       is_clang_required = True
     if not is_clang_required:
       return 0
     if re.search(r'\b(make_clang_dir)=', os.environ.get('GYP_DEFINES', '')):
       print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
       return 0
 
+  if use_head_revision:
+    # TODO(hans): Remove after the next roll.
+    global VERSION
+    VERSION = '3.9.0'
+
   global CLANG_REVISION, PACKAGE_VERSION
   if args.print_revision:
     if use_head_revision:
       print GetSvnRevision(LLVM_DIR)
     else:
       print PACKAGE_VERSION
     return 0
 
   if args.print_clang_version:
     sys.stdout.write(VERSION)
@@ skipping 13 matching lines @@
     args.force_local_build = True
     if 'OS=android' not in os.environ.get('GYP_DEFINES', ''):
       # Only build the Android ASan rt on ToT bots when targetting Android.
       args.with_android = False
 
   return UpdateClang(args)
 
 
 if __name__ == '__main__':
   sys.exit(main())