Fix gcc 9 deprecated copy warnings in antistable.

include/boost/move/algo/predicate.hpp

@@ -28,6 +28,10 @@ struct antistable
       : m_comp(comp)
    {}
 
+   antistable(const antistable & other)
+      : m_comp(other.m_comp)
+   {}
+
    template<class U, class V>
    bool operator()(const U &u, const V & v)
    {  return !m_comp(v, u);  }