[clang] [flang] [flang][Driver] Let the linker fail on multiple definitions of main() (PR #73124)

[Michael Klemm via cfe-commits]

mjklemm wrote:

Folks, I have made another attempt to improve this patch.  @kparzysz with your feedback in mind, I have now added a check if `--whole-archive` is active for some reason.  If so, flang will not add it to the link line again.

https://github.com/llvm/llvm-project/pull/73124