https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91742
--- Comment #4 from Diego Franco <di...@franco-technologies.com> ---
> It's not implementation defined, but I think all implementations are required
> to do what GCC 8 does (and other compilers agree).
It worked on linaro 7.4.1 gcc with c++17, gcc 7.1.0 with c++17 only.
> If "const X& b2 (a)" is used instead of list-init, the second assertion
> passes.
That seems like an issue no working with {}.
