[llvm] [dsymutil][DWARFLinker] Refactor handling mergeable libraries. (PR #80615)

[via llvm-commits]

fredriss wrote:

I don't think this new approach covers all cases. The initial implementation of llvm-dsymutil didn't care about relocations and would just go through the Dwarf and patch things that looked like they needed patching like the low_pc of functions. I discovered that these are however not the only places where relocations occur. Global variables have relocations too, and weirdly I've seen relocations in the middle of a complex Dwarf location expression. Falling back on actually relocation processing was the way we handled these cases.

https://github.com/llvm/llvm-project/pull/80615