[llvm] [llvm][Support][Windows] Fix slash in path for remove_directories (PR #121448)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo approved this pull request.

LGTM, thanks.

Do you think it would be feasible to hit this case in one of the unit tests? IIRC the existing unit test already tests a number of tricky corner cases relating to this implementation.

https://github.com/llvm/llvm-project/pull/121448