Vector is not trivially copyable

[krzikalla]

If you change

https://github.com/VcDevel/Vc/blob/b84dcd0a65d8dc5de6a2bd4d367882b3748f812c/Vc/common/simdarrayfwd.h#L49-L54

to

    Vc_INTRINSIC Vector(const Vector &x) = default;
    Vc_INTRINSIC Vector &operator=(const Vector &x) = default;

Vector and in turn SimdArray becomes trivially copyable. Currently we get a lot of warnings with gcc 11.2, if we use Vc types together with memcpy (which we can't change). I don't see any problems resulting in the proposed change.