[llvm] [LoopUtils] prevent negative estimated trip count result (PR #195610)

[Arda Serdar Pektezol via llvm-commits]

pektezol wrote:

> Hmm, that at least affects what is printed by the `LLVM_DEBUG`. Does it corrupt the value before `getLoopEstimatedTripCount` returns it as an `unsigned`?

Well, no. But in the `LoopPeel` case, where if the `EstimatedTripCount + AlreadyPeeled` is equal to 0, the pass peels until `EstimatedTripCount` which is INT_MAX--which effectively hangs opt.


https://github.com/llvm/llvm-project/pull/195610