[clang] [flang] [flang][driver] Support -gdwarf-N option. (PR #158314)

[Abid Qadeer via cfe-commits]

abidh wrote:

> Do you expect to land the code that handles this option relatively soon? If so, adding a warning indicating that the option is accepted but not handled is unnecessary, but if not, @anchuraj's suggestion is reasonable.

Yes, I plan to add that functionality this week.

https://github.com/llvm/llvm-project/pull/158314