https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99708
--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Perhaps another possible test could be ieee128_float_type_node != ibm128_float_type_node because whenever those two are different, we know __ieee128 and __ibm128 are supported (but still need to verify whether __float128 macro is defined).
