[clang] [Windows] Add git-clang-format wrapper bat file (PR #69228)

[Björn Schäpers via cfe-commits]

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+py -3 git-clang-format %*
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HazardyKnusperkeks wrote:

What is `py`? I have no program called `py` on my machine (Windows with msys2), so you would possibly break that? Why not write `python` or `python3`?

https://github.com/llvm/llvm-project/pull/69228