[clang] [flang] [Flang] RFC: Add support for -w option (PR #90420)

[Kiran Chandramohan via cfe-commits]

kiranchandramohan wrote:

Thanks @jeffhammond. I will wait for @klausler to submit https://github.com/llvm/llvm-project/pull/90518 which will make it easier for the driver and will provide more fine-grained control of warnings.

https://github.com/llvm/llvm-project/pull/90420