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

[Saleem Abdulrasool via cfe-commits]

compnerd wrote:

> > I can absolutely see the value in the opposite - minimise the ABI surface. For many projects, there is a split of internal and external headers. The idea is that this tool is only run on the external headers, so those are meant to be ABI.
> 
> There were multiple internals headers I had to annotate because tests were using there API.

Right, if there are internal headers, the developer can make the call on those, but you should use a different annotation for those as they are not meant to be public ABI. If they are included under debug or some other condition that is not present on production builds, that should be fine, but otherwise, we are extending the public ABI surface of the library.

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