[llvm] [RISCV] Cost casts with illegal types that can't be legalized (PR #153030)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Thanks for fixing it quickly. I wonder if we should split cast.ll into smaller files?

Potentially, there's quite a few RISC-V configurations we should probably be testing which would result in a lot of check lines. I'm not sure what's the best way to split them up. One file per instruction being tested?

https://github.com/llvm/llvm-project/pull/153030