[llvm] [MemDep] Mark deps as `Dirty` on translation failure as opposed to `Unknown` (PR #125741)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

It looks like this has significant compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=223989cc09dab8b524649d67f0521659fd15cfec&to=501bcc5b49202d9a7b1c0ada55d13be993b29f38&stat=instructions:u

Presumably that's why unknown is used here.

https://github.com/llvm/llvm-project/pull/125741