[Bug c++/81279] variadic template regression : compiles without error under 5.4.0 , 6.3.0 with error under 7.1.0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81279

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC before 7.1 had a bug where it would think all _call were template functions
while inside the template function _call.  So now GCC does the correct thing
and does not think that.
So before trying calling the non template form of _call would not have worked.