[Bug c++/70401] [c++1z] variadic template failed

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70401

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
We should add c++17 testing into check-c++, not everybody tests with
check-c++-all.