[llvm] [LIT] Workaround the 60 processed limit on Windows (PR #157759)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

> Are you able to add unit tests for the logic that figures out the number of pools to create/workers per pool, and the logic that distributes the tests? It looks correct to me after spending some time thinking about it, but I would rather not rely on my thinking being correct.

Right, I tried it locally by changing the `WINDOWS_MAX_WORKERS_PER_POOL` value to a smaller number, using various number of workers, and checking the distribution of workers in the pools :)

I added a test!

https://github.com/llvm/llvm-project/pull/157759