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

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index ab8e9894793a2d3c017d2a659cfeb9237a7e31b0..56e1010ba3d80b86ec04593372836216a9866d27 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -415,8 +415,9 @@ def UpdateClang(args):
     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 + [
@@ -533,6 +534,9 @@ def main():
         [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.')