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

[David Spickett via llvm-commits]

DavidSpickett wrote:

This is a bit of an RFC given that there's only one flang option that requires this that I know of. So this could be too much complication now. Since I was in the area I figured I'd try it anyway, we can always attach this to an issue for later use if necessary.

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