compile in the absence of libxml2-dev

src/kernel/config.c

@@ -740,7 +740,9 @@ void kernel_done(void)
     /* calling this function releases memory assigned to static variables, etc.
      * calling it is optional, e.g. a release server will most likely not do it.
      */
+#ifdef USE_LIBXML2
     xml_done();
+#endif
     attrib_done();
     item_done();
     message_done();