[llvm] [clang-repl] Support XDG state directory for history (PR #223037)

[Jared Wyles via llvm-commits]

jaredwy wrote:

We certainly shouldn't be updating a default output directory with out a discussion and at least an update to documentation and release notes. I would push back up updating the default directory with out good reason. 

I also don't think we should have different directories for different OS. 

https://github.com/llvm/llvm-project/pull/223037