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

[jason at gcc dot gnu.org]

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

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Passing a non-POD to a varargs function is conditionally-supported, with
implementation-defined semantics.  In GCC 5 it's supported and treated like
normal pass-by-value.  You can get a diagnostic about it with
-Wconditionally-supported.