[llvm] [llvm-ar][Object] Use K_GNU instead of K_COFF for archives with no symtab. (PR #82898)

[Jacek Caban via llvm-commits]

cjacek wrote:

Looking at this again, it probably makes sense to commit together with relanding #82642. We need parts of that for this PR to be testable, while this PR would need to land first to not break tests with #82642. I force-pushed a commit that contains both (previously reviewed) #82642 and fixes from this PR.

Is it okay to push it like that?

https://github.com/llvm/llvm-project/pull/82898