Add support for Windriver's Diab v4 (stricter C89)

src/net.h

@@ -14,11 +14,11 @@ struct mg_dns {
 };
 
 struct mg_addr {
-  union {    // Holds IPv4 or IPv6 address, in network byte order
+  union {  // Holds IPv4 or IPv6 address, in network byte order
     uint8_t ip[16];
     uint32_t ip4;
     uint64_t ip6[2];
-  };
+  } addr;
   uint16_t port;     // TCP or UDP port in network byte order
   uint8_t scope_id;  // IPv6 scope ID
   bool is_ip6;       // True when address is IPv6 address