[Bug c++/58910] std::Tuple_impl is non constexpr when using identical userdefined structs as template-args

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58910

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Indeed. Let's play safe and add a testcase before closing the bug as fixed for
5+.