[clang] [REAPPLY][Clang-Repl] Add support for out-of-process execution. #110418 (PR #144064)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I'd like to second Teresa's feedback. I'm working on Clang tests that normally take 4-5 seconds to run. This patch added 22 seconds of overhead to each lit invocation (average of 10 runs), making the experience significantly worse for me. It's not easy for me to ignore lit and run tests manually, because each has 7 RUN lines all of which differ in a non-trivial way.

https://github.com/llvm/llvm-project/pull/144064