fix for cosmic and C++17

src/xml-cxx/xml.hxx

@@ -478,7 +478,7 @@ namespace xml {
       ~stream_error() noexcept;
       const char* what() const noexcept;
     private:
-      std::istream::streampos _pos;
+      std::streampos _pos;
       Tag* _tag;
       char _char;
   };