[clang] [CodeGen] Mark weak vtables unnamed_addr on duplicable-vtable targets (PR #205930)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

I didn't thought the linkage of vtable is related to targets.

> On Mach-O, a weak vtable that is unnamed_addr lowers to a .weak_def_can_be_hidden definition

Is this only possible on Mach-O? I mean, if this is an optimization, why didn't it work on other platforms?

https://github.com/llvm/llvm-project/pull/205930