[llvm] [RISCV][SelectionDAG] Sign extend splats of i32 in getConstant on RV64 (PR #67027)

[Philip Reames via llvm-commits]

preames wrote:

This seems reasonable, but I'd like a second opinion from someone more knowledgeable.  Maybe @topperc?

https://github.com/llvm/llvm-project/pull/67027