Add stddef.h to util.h to avoid duplicate offsetof() def.

In el9 releases, our includes declare offsetof() before our header
chain includes stddef.h, which doesn't properly check if offsetof
is already defined, leading to a redefinition. Just include stddef
at all times here.

Signed-off-by: Auke Kok <auke.kok@versity.com>

utils/src/util.h

@@ -2,6 +2,7 @@
 #define _UTIL_H_
 
 #include <unistd.h>
+#include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>