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

[Leandro Lupori via cfe-commits]

https://github.com/luporl commented:

I think this can be useful, to make it possible to customize flang help messages, even though only one flang option requires it at the moment.

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