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

[Daniel Chen via cfe-commits]

DanielCChen wrote:

I see. So Fortran and C interoperability of F2003/F2008 is not supported yet in Flang? Those ~100ish regression test cases we have were passing before this PR though. 
Unfortunately, those test cases are not made public available yet. I think I can copy the source code of one test case here, but it needs to be run manually. Please let me know if that is desired to help debug the reason of the regression.

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