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

[Michael Klemm via cfe-commits]

mjklemm wrote:

@tblah @rj-jesus https://github.com/llvm/llvm-project/pull/74139 has landed.  Can you please see if `-fno-fortran-main` helps to resolve your bugs?  I will write up a blog article about this and publish it.  Maybe it would be worth documenting this as a question on StackOverflow, too?

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