[llvm] [RISCV][ISelLowering] Use Zicond for FP selects on Zfinx/Zdinx (PR #169299)

[Sam Elliott via llvm-commits]

lenary wrote:

Your concerns are right, and that's partly what i wanted to see with the testing. I'm glad you also caught the crash :)

The branch version can also make further savings in longer sequences, where the final pair of `mv`s might not need to be emitted.

I think you should probably skip this optimisation for rv32_zdinx.

Aside: One thing we're pretty useless at with rv32_zdinx is using `FSGNJ.D` to move pairs of registers, as your examples show

https://github.com/llvm/llvm-project/pull/169299