[lld] [llvm] [RISCV][LLD] Add RISCV zcmt optimise in linker relaxation (PR #77884)

[Simon Cook via llvm-commits]

https://github.com/simonpcook requested changes to this pull request.

I tried integrating this into a LLVM build locally, and there are a couple of issues that need fixing which I've commented on the appropriate lines.

https://github.com/llvm/llvm-project/pull/77884