[llvm] LV: clamp VF with TC only when scalar epilogue is needed (PR #91253)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

I've thought through the problem some more, experimented with different changes to see the failing tests, and have a proper fix now. I can confirm that the changed RISCV tests have the same cost as before. The patch is more of a cleanup patch now, as #93300 is the main patch.

https://github.com/llvm/llvm-project/pull/91253