fixing build bustage for mingw & vc7

nsprpub/pr/include/md/_win95.h

@@ -55,6 +55,9 @@
 #define _PR_INET6_PROBE
 #ifndef _PR_INET6
 #define AF_INET6 23
+/* newer ws2tcpip.h provides these */
+#ifndef AI_CANONNAME
+#define AI_CANONNAME 0x2
 struct addrinfo {
     int ai_flags;
     int ai_family;
@@ -65,7 +68,7 @@ struct addrinfo {
     struct sockaddr *ai_addr;
     struct addrinfo *ai_next;
 };
-#define AI_CANONNAME 0x2
+#endif
 #endif
 #define _PR_HAVE_THREADSAFE_GETHOST
 #define _PR_HAVE_ATOMIC_OPS