[llvm] [Support] Use std::filesystem::remove_all() in remove_directories() (PR #119146)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> @mstorsjo Does the log show what the dir paths looked like in the handing test?

The log didn't show anything about it, but I tried in a local build and added a printout before calling it, and the path is `C:\msys64\tmp\file-system-test-e3791e/DirNameWith19Charss` - so nothing very problematic (no UNC paths or anything like that).

https://github.com/llvm/llvm-project/pull/119146