[llvm] [lit] Fix lit hang on pool join when exception is thrown (PR #131881)

[David Garcia Orozco via llvm-commits]

ayylol wrote:

Hello @jh7370, wanted to get the ball rolling on the review for this fix. Figured you might be the right person to bug since I saw you review a couple of other lit related PRs. Thanks :)

https://github.com/llvm/llvm-project/pull/131881