[clang] [clang-repl] fix vtable symbol duplication error (closes #141039) (PR #185648)

[via cfe-commits]

conrade-ctc wrote:

@vgvassilev Can you take a look at this one? Fixes the duplication symbol issue for a virtual def outside the class (for clang-repl). @Vipul-Cariappa for viz as well, as he logged the original issue.

(FYI, claude was rather helpful in getting this basically one-line fix...)

https://github.com/llvm/llvm-project/pull/185648