[llvm] [SCEVExpander] Do not reuse disjoint or (PR #80281)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

Mostly to make sure I understand this properly, an alternate fix here would be to treat the or as needing it's poison generating flags dropped, and then mutate the or to an add in the same place we're dropping metadata right?

https://github.com/llvm/llvm-project/pull/80281