[clang] [Driver] Link Flang runtime on Solaris (PR #65644)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space approved this pull request.

LGTM, thanks for all the improvements!

Before merging, could you update the summary and briefly mention the additional changes made here? Otherwise people might think that these changes are required, but that's not strictly the case.

https://github.com/llvm/llvm-project/pull/65644