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

[via llvm-commits]

goldsteinn wrote:

NB: I'm not particularly familiar with this area of the code. The change seems sensible, but there very well may be side-effects I am oblivious too.

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