[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 mean, looking at the code, as far as I can tell, we always call GetAddrOfVTT immediately before EmitVTTDefinition, so setGVProperties() has already run, so running it again shouldn't do anything... unless somehow EmitVTTDefinition is overwriting the visibility, or setGVProperties() behaves differently for declarations vs. definitions.  If something like that is happening, I'd like to explicitly document it.

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