[Bug libstdc++/100992] Wrong result for is_constructible for const ref of tuple of tuples

[tkaminsk at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100992

--- Comment #6 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
To communicate more clearly, the check fails in GCC11.1 and GCC11.4
static_assert(std::is_constructible_v<F, const std::tuple<std::tuple<F>>&>);

And equivalent constructor is also ill-formed since GCC11.4:
const std::tuple<std::tuple<F>> ttup{std::tuple<F>(f1)};
F f3{ttup};

So the is_constructible_v resul matches actual constructor now.