[llvm] [LV] Ignore some costs when loop gets fully unrolled (PR #106699)

[David Sherwood via llvm-commits]

https://github.com/david-arm commented:

Thanks for addressing previous comments @igogo-x86! I have a few more comments - I'm most worried about the changes to the RISCV tail-folding tests.

https://github.com/llvm/llvm-project/pull/106699