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

[Reid Kleckner via cfe-commits]

rnk wrote:

I think it makes sense to focus on Saleem's use case, which, perhaps to translate it into Posix-ecosystem terms, is to create a single Clang DSO (similar to llvm-dylib or whatever we call it) that all the affiliated monorepo Clang tools use (clang-tidy, clang-rename, clang-format, clang-scan-deps, LLDB, whatever you like). That requires annotating private APIs that **are not for out of tree users** as being exported, which matches the status quo of linking the Clang tools statically. We don't want there to be too much divergence between the static and dynamic builds of these Clang tools, so that's going to require spraying these annotations fairly widely without implying that they are publicly facing stable APIs.

I believe this is something that Linux distributions have wanted for a long time, and something they struggle with currently. Maybe Tom @tstellar could give us some additional perspective on their goals and requirements.

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