[clang] [flang] [Flang][Driver] Deprecate Ofast (PR #101701)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu commented:

Mimicking gfortran's behavior for now seems reasonable to me. We can always update the warning message later if needed.

Thanks Kiran!

https://github.com/llvm/llvm-project/pull/101701