Solaris 2.6 has the prototypes for inet_pton() and inet_ntop() in

resolv.h.

plugins/sudoers/interfaces.c

@@ -29,6 +29,10 @@
 #include <unistd.h>
 #include <netinet/in.h>  
 #include <arpa/inet.h>
+#ifdef NEED_RESOLV_H
+# include <arpa/nameser.h>
+# include <resolv.h>
+#endif /* NEED_RESOLV_H */
 #include <netdb.h>
 #include <errno.h>