[llvm] [GISel][RISCV] Add G_CTLS Opcode and combines, lower to cls(w) (PR #175069)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > Can you now remove the FIXME patterns from AArch64InstrInfo.td added in #174367?
> 
> If I add aarch64 legalizer info, yes. I was thinking of that as a follow up though, should I also include that here?

Yes please

https://github.com/llvm/llvm-project/pull/175069