[clang-tools-extra] Allow to pass config file to clang-tidy-diff (PR #75457)

[Piotr Zegar via cfe-commits]

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@@ -128,6 +128,11 @@ Improvements to clang-tidy
   as a value for `-export-fixes` to export individual yaml files for each
   compilation unit.
 
+- Improved :program:`clang-tidy-diff.py` script. It now accepts a `-config-file` option
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PiotrZSL wrote:

There is already entry for clang-tidy-diff.py, this could be appended there & maybe refactored to avoid constant "It now".

https://github.com/llvm/llvm-project/pull/75457