[clang] [CodeGen] [VTable] don't think linkonce vtable as unique (PR #197855)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt requested changes to this pull request.

The code changes look good by the dynamic-cast-exact-disabled.cpp change is not correct - it is meant to test that the exact match optimization is not performed, but from the current test change it looks like the current test is incorrect w.r.t the actual correct behavior.

https://github.com/llvm/llvm-project/pull/197855