[clang] [CLANG] Full support of complex multiplication and division. (PR #81514)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

> @AaronBallman what do you think about the warnings (and the rest of course)?
> -fcomplex-arithmetic=full -ffast-math generates this warning: "use of nnan or ninf flags in the presence of '-fcomplex-arithmetic=full' option".
> -ffast-math -fcomplex-arithmetic=full generates this warning: "overriding '-fcomplex-arithmetic=basic' option with '-fcomplex-arithmetic=full' 
> -ffast-math sets the range to "basic" and when "full" is met. the value of range is overridden, hence the warning. Is it OK that the warnings are not symmetrical? Should we generate the first warning also for the second case or is it too redundant?

I think the second diagnostic would be pretty confusing to users because it doesn't mention `-ffast-math` and the command line doesn't mention `-fcomplex-arithmetic-basic`. It might be tricky to improve this though. CC @MaskRay

https://github.com/llvm/llvm-project/pull/81514