[lld] [ELF] Move target-specific synthetic sections into Arch/ files (PR #184057)

[Peter Smith via llvm-commits]

smithp35 wrote:

> OK, extracted "TargetInfo::initTargetSpecificSections" to #184292 . Will move the classes one arch at a time to hopefully help `git blame -C -C`.

I think I missed approving this patch after #184292 landed. Looks like a NFC rebase is needed, but I'll set approved as all the comments I had were addressed.

https://github.com/llvm/llvm-project/pull/184057