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

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h-vetinari wrote:

For anyone (like me) having to deal with correctly linking Fortran_main with flang 18+, it's worth noting that much of this got removed again in https://github.com/llvm/llvm-project/commit/8d5386669ed63548daf1bee415596582d6d78d7d.

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