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

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

This look like a good direction. I wanted to hear from @efriedma-quic before we move forward. 

@aaronj0, @Vipul-Cariappa we should test if backporting that patch to cling and removing the relevant workarounds in BackendPasses.cpp still makes cling happy. 

cc: @hahnjo 

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