[lld] [lld][ELF] Implement merged .debug_names section. (PR #86508)

[via llvm-commits]

cmtice wrote:

Except for maskray's request re using 'rm -rf %t && split-file %s %t && cd %t' in tests (still looking into that), I think I have addressed all the review request/comments. So it's ready for any additional reviewing.

If I've overlooked something please let me know.

Re @ayermolo 's suggestion to pull the DebugNames work out of SyntheticSections.cpp into another file: That's a decision I would want to leave to @MaskRay .  I don't know how much doing so would really help, however. The DebugNamesSection work in SyntheticSections.cpp is only ~750 lines, and it's all contiguous...

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