Only enable AI_IDN if it is actually defined.

Upstream-status: Pending
--- libparistraceroute-0.93.orig/libparistraceroute/address.c
+++ libparistraceroute-0.93/libparistraceroute/address.c
@@ -37,8 +37,6 @@
 
 #endif
 
-#define AI_IDN        0x0040
-
 static void ip_dump(int family, const void * ip, char * buffer, size_t buffer_len) {
     if (inet_ntop(family, ip, buffer, buffer_len)) {
         printf("%s", buffer);
@@ -58,7 +56,9 @@
     // Initialize hints
     memset(&hints, 0, sizeof(hints));
     hints.ai_family = family;
+#ifdef AI_IDN
     hints.ai_flags = AI_IDN;
+#endif
 
     // Convert string hostname / IP into a sequence of addrinfo instances
     if ((ret = getaddrinfo(hostname, NULL, &hints, &res)) != 0) {