src: define AI_V4MAPPED for OpenBSD

OpenBSD doesn't define AI_V4MAPPED by default. Defining it to 0
as done with other ports.

PR-URL: nodejs#427
Reviewed-By: Ben Noordhuis <[email protected]>

Author: qbit

src/cares_wrap.cc

@@ -24,6 +24,9 @@
 # include <arpa/nameser.h>
 #endif
 
+#if defined(__OpenBSD__)
+# define AI_V4MAPPED 0
+#endif
 
 namespace node {
 namespace cares_wrap {