[llvm] LoopVectorize: add test for #47665, #88802 (PR #91135)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Done, although I have enough space in the title to keep "LoopVectorize", which I personally prefer for the purposes of searching.

https://github.com/llvm/llvm-project/pull/91135