https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108059
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
FWIW a workaround for most valid code is to replace e.g. ignore_index_t<v>,
where v is the problematic NTTP argument, with ignore_index_t<decltype(v){}>.
