[llvm] [LV][EVL] Generate negative strided load/store for reversed load/store (PR #123608)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. Probably best to wait for @fhahn or @alexey-bataev to review it too

https://github.com/llvm/llvm-project/pull/123608