os-util: add missing headers

For 'bool' and 'usec_t'.

src/basic/os-util.h

@@ -1,8 +1,11 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <stdbool.h>
 #include <stdio.h>
 
+#include "time-util.h"
+
 /* The *_extension_release flavours will look for /usr/lib/extension-release/extension-release.NAME
  * in accordance with the OS extension specification, rather than for /usr/lib/ or /etc/os-release. */