Add sys/stat.h for S_IFDIR

Fixes
../git/src/shared/mkdir-label.c:13:61: error: use of undeclared identifier 'S_IFDIR'
        r = mac_selinux_create_file_prepare_at(dirfd, path, S_IFDIR);

Signed-off-by: Khem Raj <raj.khem@gmail.com>

src/shared/mkdir-label.c

@@ -1,5 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
+#include <sys/stat.h>
+
 #include "mkdir-label.h"
 #include "selinux-util.h"
 #include "smack-util.h"