[flang] [clang] [flang][driver] Add -fno-fortran-main (link time) option to remove Fortran_main from link line (PR #74139)

[Andrzej Warzyński via cfe-commits]

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

I'm making two more small suggestions, but these are nits. Fell free to ignore.

LGTM, thank you!

[nit] "legacy flang" --> "Classic Flang" (in summary)

https://github.com/llvm/llvm-project/pull/74139