[RISCV] Add back handling of X > -1 to ISD::SETCC lowering.

There are cases where the -1 doesn't become visible until lowering
so the folding doesn't have a chance to run.

I think in these cases there is a missed DAGCombine for truncate (undef),
which I may fix separately, but RISC-V backend should protect itself.

Fixes #64503.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D157314