Add declarations to tests headers

tests/ui/stub_ui.c

@@ -457,6 +457,7 @@ void cons_outtype_setting(void) {}
 void cons_intype_setting(void) {}
 void cons_gone_setting(void) {}
 void cons_history_setting(void) {}
+void cons_carbons_setting(void) {}
 void cons_log_setting(void) {}
 void cons_chlog_setting(void) {}
 void cons_grlog_setting(void) {}