[clang] Clang tooling generated visibility macros for Clang (PR #109702)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I'd like some answer about how we plan to ensure the macros remain correct.  Short-term, "someone periodically runs the tool manually" might be good enough if we don't expect much churn, I guess.

Also, can the tool itself be added to llvm-project?

(The actual changes seem fine at first glance, but I haven't tried to dive deep into the specifics of what exact symbols get exported as a result of the macros.)

https://github.com/llvm/llvm-project/pull/109702