[clang] [clang codegen][regression] Add dso_local/hidden/etc. markings to VTT definitions and declarations (PR #72452)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I'd prefer not to call setGVProperties() twice on the same variable; under what conditions is the first call not sufficient?

https://github.com/llvm/llvm-project/pull/72452