[llvm] [LV] Pre-commit test for #128062 (PR #164801)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> Did you check this works as expected? I think to trigger narrowInterleaveGroups, a target-specific test is needed, as it checks the size of the vector against the target vector size.

I got a diff with https://github.com/llvm/llvm-project/pull/164839, although that PR needs more thought?

https://github.com/llvm/llvm-project/pull/164801