[Bug c++/64867] warning for passing non-POD to varargs function

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64867

--- Comment #12 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. trivially-copyable is not the same as trivial (and there are separate type
traits for testing those two properties).