WINGs: Add support for syslog messaging

This patch is used to add support for syslog messaging implemented in
WINGs lib directly, so available from the lib itself and wmaker too.
I believe it will in a first time help to get some logging info
centralized in one point, and in a second time maybe add some info
level messages like wmaker is starting, stopping, restarting and else.

For now, it's built by default when the syslog support is found, maybe
we could also disable it by default.

src/main.c

@@ -201,6 +201,8 @@ noreturn void Exit(int status)
 	if (dpy)
 		XCloseDisplay(dpy);
 
+	wutil_shutdown();  /* WUtil clean-up */
+
 	exit(status);
 }