[llvm] [Vectorizer] fix GEPs incorrectly marked as "inbounds" (PR #120730)

[Florian Hahn via llvm-commits]

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

LGTM, thanks.

Might be worth adjusting the title using [LV] instead of [Vectorizer] (which is more ambiguous) and maybe adding a bit more detail, something like

`[LV] Drop inbounds for reverse vector pointers when folding tail.`

https://github.com/llvm/llvm-project/pull/120730