[clang] [flang] [flang][driver] Introduce FCC_OVERRIDE_OPTIONS. (PR #140556)

[Tarun Prabhu via cfe-commits]

tarunprabhu wrote:

> > Does `CCC_OVERRIDE_OPTIONS` expands to Clang Compiler Commandline Override Options? If so `FCC_OVERRIDE_OPTIONS` expanding to Fortran Compiler Commandline Override Options seems the right replacement.
> > If `CCC_OVERRIDE_OPTIONS` expands to Clang C Compiler Override Options then `FFC_OVERRIDE_OPTIONS` (as suggested by @tarunprabhu) expanding to Flang Fortran Compiler Overrided Options is better.
> 
> I am happy with either of them.

Maybe we should split the difference and call it `FFF_OVERRIDE_OPTIONS`. More Fortran for everyone! :-)

https://github.com/llvm/llvm-project/pull/140556