[lld] [lld][ELF] Add --debug-names to create merged .debug_names. (PR #86508)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks for adding `updateMultiCuOffsets`. I am glad that multi-CU testing (`debug-names-multi-cus.s`) did expose a bug.
However, `updateMultiCuOffsets` does a lightweight parsing of `.debug_info` and still ignores `.debug_info + X` relocations in `.rela.debug_names`, and the current implementation does not handle 3+ CUs correctly.

I have tried a relocation-based support in the top commit of https://github.com/MaskRay/llvm-project/tree/lld-debug-names, which should hopefully fix the issue.

https://github.com/llvm/llvm-project/pull/86508