[lld] [LLD][COFF] Handle imported weak aliases consistently (PR #109105)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

I'll go ahead and merge this right away, as there's another patch in the queue touching the same areas, to simplify conflicts in that area. (Otherwise I would maybe have left the patch for 24h, for people in other time zones to comment on. But this change feels mostly straightforward to me.)

https://github.com/llvm/llvm-project/pull/109105