https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106652
--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> --- What I did in the patch is stop predefining __FLT32X_*__ macros etc. for C++ because C++ doesn't support those, so perhaps the if !__GNUC_PREREQ (7, 0) || defined __cplusplus conditions related to _Float<N> (but not _Float<N>x) could be fixincluded or changed to if !__GNUC_PREREQ (7, 0) || (defined __cplusplus && defined __FLT32_MANT_DIG__) or so (to differentiate between C++ doesn't have vs. has _Float<N> keywords.
