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

[Alpha Abdoulaye via llvm-commits]

Alpha-10000 wrote:

> I did not understand what should be done for the tests. Could you point for the relocation map reference which should be deleted, please?
All the `.dSYM` files under `test/tools/dsymutil/Inputs/`, with the `Contents/Resources/Relocations/` directory


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