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

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> Can we add a test that shows the issue from real code?

@mikhailramalho feel free to use [this test reduced from perlbench](https://github.com/michaelmaitland/llvm-project/blob/cfb65551f148e39e33311f77d6fc364cfaca3473/llvm/test/CodeGen/RISCV/simplify-condbr.ll)

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