[core] ignore server.event-handler = "libev"

ignore server.event-handler = "libev" if lighttpd not built with libev
(no longer an error)

On most platforms, native event handling in lighttpd is more performant
than the overhead of libev, which usually uses the same underlying
OS system interface for event notification

src/fdevent.c

@@ -57,6 +57,11 @@ int fdevent_config(const char **event_handler_name, log_error_st *errh) {
 	const char * event_handler = *event_handler_name;
 	fdevent_handler_t et = FDEVENT_HANDLER_UNSET;
 
+#ifndef FDEVENT_USE_LIBEV
+	if (NULL != event_handler && 0 == strcmp(event_handler, "libev"))
+		event_handler = NULL;
+#endif
+
 	if (NULL == event_handler) {
 		/* choose a good default
 		 *