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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

> I never heard about Itanium-Apple before..

I don't think anyone calls it that formally; I was just using it as a shorthand for "the variant of the Itanium C++ ABI used on Apple platforms".

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