Add compound operators for builtin types value modification

[mborland]

Such as

template <std::floating_point T>
T& operator+=(T& lhs, const boost::int128::int128& rhs) {
    lhs = /* ... */;
    return lhs;
}

template <std::integral T>
T& operator|=(T& lhs, const [my_big_int](boost::int128::int128)& rhs) {
    lhs = /* ... */;
    return lhs;
}