[llvm] [SelectionDAG] Avoid illegal wide vectors expanding get.active.lane.mask (PR #213670)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

How come we're seeing get.active.lane.mask being generated on RISC-V? I thought the loop vectorizer always emitted a step-vector + icmp on RISC-V unless it was overridden by the `-force-tail-folding-style` flag

https://github.com/llvm/llvm-project/pull/213670