[llvm] [llvm][Support][NFC] Disentangle SpecialCaseList parsing and matching (PR #116800)

[Boaz Brickner via llvm-commits]

https://github.com/bricknerb requested changes to this pull request.

I guess my main feedback is that I think we should try to move all changes that are not disentanglement specific to separate PRs.
Are all error strings covered with tests so we can assume that if tests pass we haven't didn't impact any error?

https://github.com/llvm/llvm-project/pull/116800