[llvm] [LV] Don't require scalar epilogue for unsupported IAG with tail (PR #96544)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> I was considering that option too, but groups are constructed for entire loop and one group can be valid with one VF, but not valid with the other. That said, invalidation is illegal when VPlans with and without interleaved groups are in flight. Only when specific VPlan is selected, invalidation can take place.

Make sense, thanks.

https://github.com/llvm/llvm-project/pull/96544