Always call finalizer for stack classes. Checking for the number of destructors of the class type is not sufficient: we may be holding a derived class with a destructor. Fixes: run/auto_07

module union1;

union U
{
    float f;
    int i;
}

void main()
{
    float f = 2;
    U u = U(f);
    assert(u.i == *cast(int*)&f);
}