[clang] [RISCV][LLD] Add RISCV zcmt optimise in linker relaxation (PR #68551)

[via cfe-commits]

Xinlong-Wu wrote:

> > This patch is moved from https://reviews.llvm.org/D134600
> 
> Why? That loses all the context in the Phabricator review. Keep the review there.

yes, I will keep it there.

But the [Phabricator shutdown timeline](https://discourse.llvm.org/t/update-on-github-pull-requests/71540) said that 
> Phabricator becomes read-only after October 1

So I thought it may means we can't add comments or update it? That's why I moved it from Phabricator.

If you mean we still can review&update it at Phabricator, I will close this pr. )

https://github.com/llvm/llvm-project/pull/68551