Fix running package.py on Windows after https://codereview.chromium.org/1169353002

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.
 
 """Windows can't run .sh files, so this is a Python implementation of
 update.sh. This script should replace update.sh on all platforms eventually."""
 
 import argparse
 import contextlib
@@ skipping 397 matching lines @@
   binutils_incdir = ''
   if sys.platform.startswith('linux'):
     binutils_incdir = os.path.join(BINUTILS_DIR, 'Linux_x64/Release/include')
 
   # If building at head, define a macro that plugins can use for #ifdefing
   # out code that builds at head, but not at LLVM_WIN_REVISION or vice versa.
   if use_head_revision:
     cflags += ['-DLLVM_FORCE_HEAD_REVISION']
     cxxflags += ['-DLLVM_FORCE_HEAD_REVISION']
 
-  deployment_env = os.environ.copy()
+  deployment_env = None
   if deployment_target:
+    deployment_env = os.environ.copy()
     deployment_env['MACOSX_DEPLOYMENT_TARGET'] = deployment_target
 
   cmake_args = base_cmake_args + [
       '-DLLVM_BINUTILS_INCDIR=' + binutils_incdir,
       '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
       '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
       '-DCMAKE_EXE_LINKER_FLAGS=' + ' '.join(ldflags),
       '-DCMAKE_SHARED_LINKER_FLAGS=' + ' '.join(ldflags),
       '-DCMAKE_MODULE_LINKER_FLAGS=' + ' '.join(ldflags),
       '-DCHROMIUM_TOOLS_SRC=%s' % os.path.join(CHROMIUM_DIR, 'tools', 'clang'),
@@ skipping 96 matching lines @@
       stderr = None
     else:
       try:
         stderr = os.fdopen(os.dup(sys.stdin.fileno()))
       except:
         stderr = sys.stderr
     return subprocess.call(
         [os.path.join(os.path.dirname(__file__), 'update.sh')] + sys.argv[1:],
         stderr=stderr)
 
+  # Don't buffer stdout, so that print statements are immediately flushed.
+  sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
+
   parser = argparse.ArgumentParser(description='Build Clang.')
   parser.add_argument('--bootstrap', action='store_true',
                       help='first build clang with CC, then with itself.')
   parser.add_argument('--if-needed', action='store_true',
                       help="run only if the script thinks clang is needed")
   parser.add_argument('--force-local-build', action='store_true',
                       help="don't try to download prebuild binaries")
   parser.add_argument('--print-revision', action='store_true',
                       help='print current clang revision and exit.')
   parser.add_argument('--run-tests', action='store_true',
@@ skipping 38 matching lines @@
     # Use a real revision number rather than HEAD to make sure that the stamp
     # file logic works.
     LLVM_WIN_REVISION = GetSvnRevision(LLVM_REPO_URL)
     PACKAGE_VERSION = LLVM_WIN_REVISION + '-0'
 
   return UpdateClang(args)
 
 
 if __name__ == '__main__':
   sys.exit(main())