[lld] [llvm] [lld][llvm/mc] Add support for sdata8 for FDE CIE (PR #174508)

[Farid Zakaria via llvm-commits]

fzakaria wrote:

> As suggested by Peter, the lld/test test is unrelated and should be removed. Yes, we can add a cl::opt (-mllvm -xxx) for such toggles. I think it's clearer to merge #174637 into this PR (after removing the lld change). #174637 should be gated by the cl::opt option, not change the existing `sdata4` behavior for CodeModel::Medium.
> 
> If you have removed clang and lld support, please update the title and patch description (note: the git commit message is ignored)

I will remove the `lld` test and update the title.

How about after this PR lands, I rebase #174637 and incorproate the same gating.
That way we can keep the PRs separate still?

I'll also kickstart the ABI conversation; it will be from my personal email.

https://github.com/llvm/llvm-project/pull/174508