[llvm] [RISCV] Add late optimization pass for riscv (PR #133256)

[Sam Elliott via llvm-commits]

lenary wrote:

Can we call this something like "RISC-V Late Peephole Optimisation Pass" or "RISC-V Late Branch Optimisation Pass", rather than just "Late Optimisation". I don't want that to prevent us adding more things to it in the future, but I do want to have a slightly more descriptive name

https://github.com/llvm/llvm-project/pull/133256