[clang] [flang] [flang][Driver] support -fno-openmp (PR #107087)

[Tom Eccles via cfe-commits]

tblah wrote:

> As I'm not seeing how linker is invoked, I just need to ask (for the sake of completeness) will it also prevent addition of `-lomp` to the linker's command line?

Thanks for pointing this out. I've added a test for the linker invocation.

https://github.com/llvm/llvm-project/pull/107087