[lld] [ELF] Support relocatable files using CREL (PR #98115)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

Thanks for answering the question.

I think we will need to support `SHT_REL` to `CREL` conversion for relocatable links and emit-relocs will likely not be supported with `CREL` on `SHT_REL` platforms. I'm thinking that almost all links will have some files from archives like `crt0.o` that will have `SHT_REL` relocations. 

I also think we'll need to have some kind of way of either requiring input CREL relocations to have explicit addends (with diagnostic), or we support implicit addends.

I'm fine with these being limitations for an experimental CREL implementation though. We can fix these in further patches.

My last suggestion. Can we add an entry into the release notes about supporting CREL and either link or describe what the limitations are?

I'm happy to Approve after that.

https://github.com/llvm/llvm-project/pull/98115