https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115688
--- Comment #8 from Kewen Lin <linkw at gcc dot gnu.org> ---
> > -mabi={no-,}altivec is only for the 32-bit ABIs. All the 64-bit ABIs had
> > either only compatible changes to support VMX, or only ever had support for
> > it in the first place.
> In that case, -mabi=no-altivec should also be a hard error if -m64 is in
> effect.
Filed PR115714 to track.
