Include <sys/stat.h> for S_I* macros

Fix a compilation failure with musl libc.

* mknod.c: Include <sys/stat.h>.
* printmode.c: Likewise.

Reported-by: Dima Krasner <dima@dimakrasner.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/printmode.c b/printmode.c
index 4df1b9f..a721936 100644
--- a/printmode.c
+++ b/printmode.c
@@ -1,6 +1,7 @@
 #include "defs.h"
 
 #include <fcntl.h>
+#include <sys/stat.h>
 
 #include "xlat/modetypes.h"