[clang] Add ability for clang-format-diff to exit with non-0 status (PR #70883)

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``````````bash
darker --check --diff -r 2164a449dc7a9daf610b789ba0ec7d1eca7305ef..646cabcf167facb63c78277b50ea62afbc61b3c0 clang/tools/clang-format/clang-format-diff.py
``````````

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View the diff from darker here.
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``````````diff
--- clang-format-diff.py	2023-11-01 01:55:27.000000 +0000
+++ clang-format-diff.py	2023-11-01 02:10:13.409792 +0000
@@ -97,11 +97,11 @@
     )
     parser.add_argument(
         "-non-zero-exit-code",
         action="store_true",
         default=False,
-        help="exit with a non-zero status if formatting changes are necessary"
+        help="exit with a non-zero status if formatting changes are necessary",
     )
     args = parser.parse_args()
 
     # Extract changed lines for each file.
     filename = None

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https://github.com/llvm/llvm-project/pull/70883