[clang] [clang-format] convert path to Windows path if user is using a MSYS2 shell (PR #111526)

[via cfe-commits]

mydeveloperday wrote:

I personally use Cygwin and it's git understands unix paths is that not the case for msys2 or are you mixing msys2 with windows based git, won't this have the potential to break others?

https://github.com/llvm/llvm-project/pull/111526