[llvm] Initial changes for llvm shared library build using explicit visibility annotations (PR #96630)

[Vassil Vassilev via llvm-commits]

vgvassilev wrote:

FWIW, the google summer of code midterms are in 9 days and I'd very much like to converge on this PR and hopefully have it merged. That'd be good for the GSoC reporting.

https://github.com/llvm/llvm-project/pull/96630