[llvm] [RISCV] Add branch folding before branch relaxation (PR #134760)

[Mikhail R. Gadelha via llvm-commits]

mikhailramalho wrote:

Folks, I've updated the PR with an option to disable tail merging when calling the branch folding pass.

This required me to create a `createBranchFolderPass` (similar to PR #128858); I can submit a separate PR for this change if you think it's necessary.

I'll run SPEC now and report the results once it's done.

https://github.com/llvm/llvm-project/pull/134760