[lld] [ELF] Add --compress-nonalloc-section (PR #84855)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> I'd prefer `--compress-sections` as a flag name and mention in the help and documentation that it's only applicable to non-allocated sections. That gives us an option to eventually extend the implementation to allocated sections without having to introduce yet another flag (plus `--compress-sections` is easier to spell and remember).

Thanks for your feedback. I'm eager to hear others' as well.
If we go with --compress-sections, we need a warning when a SHF_ALLOC section is matched.

https://github.com/llvm/llvm-project/pull/84855