[clang] [Clang-Repl] Add custom function as lambda in launchExecutor and fetch PID of launched executor (PR #147478)

[Anutosh Bhat via cfe-commits]

https://github.com/anutosh491 approved this pull request.

Looks okay to me, let's see what other reviewers have to say.

https://github.com/llvm/llvm-project/pull/147478