[clang] [clang-tools-extra] [flang] [lld] [llvm] [flang][clang] Add Visibility specific help text for options (PR #81869)

[Leandro Lupori via llvm-commits]

luporl wrote:

> I'm a bit short on spare cycles for reviewing stuff :( @luporl , do you have time to go over this? I'll bump this on my list regardless.

@banach-space, yes, I can go over this in more details.

https://github.com/llvm/llvm-project/pull/81869