[llvm] [lit] Migrate lit to ProcessPoolExecutor (PR #202681)

[via llvm-commits]

prasoon054 wrote:

I have reverted this change for now, based on my discussion with @ilovepi @boomanaiden154 and @petrhosek 
Check here: https://github.com/llvm/llvm-project/pull/206138
We haven't been able to reproduce this on our Mac machines, both of which run on macOS 26.5.1. I will open a discourse thread where we can discuss how to get a fix for this.

https://github.com/llvm/llvm-project/pull/202681