[llvm] [Support][Windows] disk_space handle unicode paths (PR #170716)

[Aaron Ballman via llvm-commits]

https://github.com/AaronBallman commented:

These changes look correct to me and there isn't really a good way to test disk space failures, so I think we don't need any extra test coverage.

CC @zmodem @compnerd for some extra eyes in case I've missed something.

https://github.com/llvm/llvm-project/pull/170716