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

[Mikhail R. Gadelha via llvm-commits]

mikhailramalho 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)

I see that #131728 has a different version with an extra function; should I use that instead?

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