Making __builtin_signbit type-generic

[FX]

Hi,

Many of the floating point-related builtins are type-generic, including __builtin_{isfinite,isinf_sign,isinf,isnan,isnormal,isgreater,islesser,isunordered}. However, __builtin_signbit is not. It would make life easier for the implementation of IEEE in Fortran if it were, and probably for some other stuff too (PR 36757).

I don’t know where to start and how to achieve that, though. Could someone who knows this middle-end FP stuff help?

Thanks,
FX