[llvm] [LoopVectorize] Add an option to test potential issues with VPlan (PR #121154)

[Danila Malyutin via llvm-commits]

danilaml wrote:

@fhahn what do you think? Using address spaces for that feels a bit cleaner but would also require bigger changes to the LoopVectorizer.cpp (or moving the option to Loads.cpp) which I'm less comfortable with.

https://github.com/llvm/llvm-project/pull/121154