Core: guard use of AI_ADDRCONFIG.

Some systems (notably NetBSD and OpenBSD) lack AI_ADDRCONFIG support.

Reported by Piotr Sikora.
diff --git a/auto/unix b/auto/unix
index bc3c0f1..cd4209e 100755
--- a/auto/unix
+++ b/auto/unix
@@ -788,11 +788,7 @@
                   #include <netdb.h>"
 ngx_feature_path=
 ngx_feature_libs=
-ngx_feature_test='struct addrinfo hints, *res;
-                  hints.ai_family = AF_UNSPEC;
-                  hints.ai_socktype = SOCK_STREAM;
-                  hints.ai_flags = AI_ADDRCONFIG;
-                  if (getaddrinfo("localhost", NULL, &hints, &res) != 0)
-                      return 1;
+ngx_feature_test='struct addrinfo *res;
+                  if (getaddrinfo("localhost", NULL, NULL, &res) != 0) return 1;
                   freeaddrinfo(res)'
 . auto/feature
diff --git a/src/core/ngx_inet.c b/src/core/ngx_inet.c
index bb03720..0792d6e 100644
--- a/src/core/ngx_inet.c
+++ b/src/core/ngx_inet.c
@@ -963,7 +963,9 @@
     ngx_memzero(&hints, sizeof(struct addrinfo));
     hints.ai_family = AF_UNSPEC;
     hints.ai_socktype = SOCK_STREAM;
+#ifdef AI_ADDRCONFIG
     hints.ai_flags = AI_ADDRCONFIG;
+#endif
 
     if (getaddrinfo((char *) host, NULL, &hints, &res) != 0) {
         u->err = "host not found";