[llvm] [Object][Archive] Recompute headers and symbol map when switching from COFF to GNU64 (PR #160606)

[Jacek Caban via llvm-commits]

cjacek wrote:

Thanks for reviews.

> If link.exe can handle GNU files, maybe we should default to GNU in LibDriver.cpp unless we're targeting ARM64EC?

It would probably be fine in practice, but it would be a small step backward in terms of compatibility, so I’d prefer to stick with this (not a strong opinion, though).

https://github.com/llvm/llvm-project/pull/160606