Method fetch_sub

src/fl/stl/atomic.h:164–169

    }
    
    T fetch_sub(T value) FL_NOEXCEPT {
        T old = mValue;
        T temp = old - value;
        mValue = temp;
        return old;
    }
    
    T fetch_and(T value) FL_NOEXCEPT {
        T old = mValue;