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

[Owen Pan via cfe-commits]

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@@ -185,6 +191,8 @@ def main():
             diff_string = "".join(diff)
             if len(diff_string) > 0:
                 sys.stdout.write(diff_string)
+                if args.non_zero_exit_code:
+                    sys.exit(1)
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owenca wrote:

I was aware of that but doubt it woud break any valid use cases. In fact, we made similar fixes to git-clang-format without adding options. We can always revisit this if we get valid complaints.

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