[clang] [flang] [flang][driver] Add support for -isysroot in the frontend (PR #77365)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

Thank you for your continued effort to improve this!

> Anyone knows if this is expected and Visibility should be explicitly specified in each alias, to add support to flang-new, or is this an issue and the alias should have the same visibility as the original option?

IIRC, when `Visibility` is omitted then it defaults to "Clang" (or something to that effect). That would explain what you see. Something to be fixed :) 

https://github.com/llvm/llvm-project/pull/77365