[lld] [llvm] [dyndbg][LLD][ELF] Prototype LLD support for dynamic debugging (PR #190939)

[Peter Smith via llvm-commits]

smithp35 wrote:

> I have now introduced a new section type `SHT_LLVM_ELF` for the dynamic debugging section. @MaskRay and @smithp35, what do you think of this? Thanks.

I think the code looks better with the additional section type. A few thoughts:
* `LLVM_ELF` is a very general name. If this is to be specific to embedding a relocatable ELF file, perhaps something like `LLVM_EMBEDDED_ELF`.
* Is the type intended to represent a family of Embedded ELF use cases, or just this one? If it is just this one then we probably don't need to check the name and rely on the type alone.
* Although not necessary for a draft, will need documenting in the LLVM extensions https://llvm.org/docs/Extensions.html 


https://github.com/llvm/llvm-project/pull/190939