[llvm] [RISCV][ISel] Fold FSGNJX idioms (PR #100718)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp commented:

I don't know if there may be an impact, but can you test if this combine works well with Zfa?

https://github.com/llvm/llvm-project/pull/100718