Add required POSIX includes and fairly portable Unix include.

POSIX specifies that inet_ntoa() is declared in arpa/inet.h, and that
POLLRDNORM, etc. are defined in poll.h.

gethostbyname() is not specified by POSIX, but the manpages in OpenBSD,
FreeBSD, OS X, and glibc all state that it is declared in netdb.h.

Without these headers, the build fails on OpenBSD and possibly other
systems.

Source/Core/Core/IPC_HLE/WII_IPC_HLE_Device_net.cpp

@@ -6,6 +6,11 @@
 #include <cstdio>
 #include <cstdlib>
 #include <string>
+#ifndef _WIN32
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <poll.h>
+#endif
 
 #include "Common/CommonPaths.h"
 #include "Common/FileUtil.h"

Source/Core/Core/IPC_HLE/WII_Socket.cpp

@@ -4,6 +4,7 @@
 
 #include <algorithm>
 #ifndef _WIN32
+#include <arpa/inet.h>
 #include <unistd.h>
 #endif