Brad Campbell <brad@seme.com.au> notes that

xconnect.c needs #include <netinet/in.h>
to compile if CONFIG_FEATURE_IPV6 is not defined

libbb/xconnect.c

@@ -8,10 +8,11 @@
 
 #include <unistd.h>
 #include <string.h>
+#include <stdlib.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netdb.h>
-#include <stdlib.h>
+#include <netinet/in.h>
 #include "libbb.h"
 
 int xconnect(const char *host, const char *port)