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

[Henrik G. Olsson via llvm-commits]

hnrklssn wrote:

> Can you take a look?

Was asleep, sorry! But I see you fixed it with the mismatching CRs, thanks. Not sure why that didn't end up being an issue on my Windows machine; I don't use Windows very often, but I would've expected it to behave consistently.

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