https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114395
--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Right, another design principle is that () should work where {} works, and
const B &b{a}; works. A(b) previously didn't work so it's not really changing
meaning. So not a bug IMHO.
