[RISCV] Handle LHS == 0 in isVLKnownLE (#148860)

If a VL is zero then it's known to be less than or equal to every other
VL.

This looks weird on its own since a VL of zero isn't that common. The
test diffs come from a type being split resulting in a VP intrinsic's
EVL being zero.

The motivation for this is to split off part of an upcoming patch I plan
on submitting for RISCVVLOptimizer, which generalizes it to handle
recurrences, and needs to reason about an initial state of demanded VLs
set to zero.

0 files changed, 0 insertions, 0 deletions