[flang] [clang] [flang][driver] Remove Fortain_main static library from linking stages (PR #75816)

[Michael Klemm via cfe-commits]

mjklemm wrote:

> I would probably create a section on building executables and just mention that 3 runtime libs will be linked auto-magically. Unless somebody uses `-fno-fortran-main` ;-) Make it as short or as long as you prefer - your contribution is greatly appreciated 🙏🏻 :)

If have written up a first draft.  Please have a look and let me know what you think.

https://github.com/llvm/llvm-project/pull/75816