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

[Thomas Fransham via cfe-commits]

fsfod 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 because tests were using there API.

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