[Bug c++/78966] Unjustified variadic template instantiation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78966

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There is to check if there is a constructor which converts X<T>.  There might
be a C++ Defect report about this case too.