fix: port to GCC 13 (Ubuntu 24.04)

Author: knopki

Kernel/flags.h

@@ -16,6 +16,7 @@ You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, write to the Free Software
 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */
+#include <cstdint>
 
 #ifndef FLAGS_H
 #define FLAGS_H