The behavior of a program that adds specializations for
any of the templates defined in this subclause is undefined,
unless explicitly permitted by the specification of the corresponding template.
is_pod<T> is a Cpp17UnaryTypeTrait ([meta.rqmts])
with a base characteristic of true_type
if T is a POD type,
and false_type otherwise.
A POD class is a class that is both a trivial class and a standard-layout class,
and has no non-static data members of type non-POD class (or array thereof).
A POD type is a scalar type, a POD class, an array of such a type,
or a cv-qualified version of one of these types.