[llvm] fix(llvm/**.py): fix invalid escape sequences (PR #94035)

[Artem Belevich via llvm-commits]

https://github.com/Artem-B approved this pull request.

+1 to using `r""` everywhere. LGTM otherwise.

I think it's OK to include the change in the NVPTX test -- it fits with the rest of the string fixes and has nothing to do with the test functionality itself.

https://github.com/llvm/llvm-project/pull/94035