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

[via llvm-commits]

RohanOnKeys wrote:

@evanphx hello, could you pls have a look for this ? and could you pls lmk which discord channel to hop in for cllang discussions ????

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