[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

[gcc-bugzilla at contacts dot eelis.net]

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

--- Comment #6 from Eelis <gcc-bugzilla at contacts dot eelis.net> ---
Clang's libc++ (which gives the expected result) might be another source of
inspiration.