[llvm] [Utils] fix diff_test_updater on Windows (PR #158235)

[Henrik G. Olsson via llvm-commits]

hnrklssn wrote:

> How are you running the tests on your Windows machine? If inside WSL, that might be the reason why. (I run everything through the regular Windows command prompt)

I launched `Developer Command Prompt for VS 2022` as administrator in the build directory and ran: `cmake --build . -t check-lit`. I didn't run it in WSL, but I have WSL installed.

It seems like python scripts on my Windows machine somehow emits Unix line endings. The `diff-strip-trailing-cr.txt` case in `llvm/utils/lit/tests/shtest-shell.py` was also failing because it didn't diff as much as expected, but I didn't think more about the cause at the time.

https://github.com/llvm/llvm-project/pull/158235