[Bug libstdc++/56785] std::tuple of two elements does not apply empty base class optimization when one of its elements is a std::tuple with two elements

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56785

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
IIRC with libc++ tuple<> is not an empty type, so has more overhead than ours
in other edge cases. Maybe you should recommend users stay away from that too.