set some defaults for apple builds without configure script

unix.c

@@ -18,13 +18,30 @@
 #define ENET_BUILDING_LIB 1
 #include "enet/enet.h"
 
-#ifdef HAS_FCNTL
-#include <fcntl.h>
-#endif
-
 #ifdef __APPLE__
+#ifdef HAS_POLL
 #undef HAS_POLL
 #endif
+#ifndef HAS_FCNTL
+#define HAS_FCNTL 1
+#endif
+#ifndef HAS_INET_PTON
+#define HAS_INET_PTON 1
+#endif
+#ifndef HAS_INET_NTOP
+#define HAS_INET_NTOP 1
+#endif
+#ifndef HAS_MSGHDR_FLAGS
+#define HAS_MSGHDR_FLAGS 1
+#endif
+#ifndef HAS_SOCKLEN_T
+#define HAS_SOCKLEN_T 1
+#endif
+#endif
+
+#ifdef HAS_FCNTL
+#include <fcntl.h>
+#endif
 
 #ifdef HAS_POLL
 #include <sys/poll.h>