OS/400 does not support inet_aton, and thus an error occurs when trying to compile main/network.c.  

I did notice that ext/standard/flock_compat.c has an implementation of inet_aton. And that main/network.c does include the prototype as follows:

#ifndef PHP_WIN32
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#else
int		 inet_aton(const char *, struct in_addr *);
#endif


All I ask is to change the above to the following:

#ifndef PHP_WIN32
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#endif

#ifndef HAVE_INET_ATON
int		 inet_aton(const char *, struct in_addr *);
#endif