libudns: add definition to enable IPv6 support

This is an option in the origin configure script, add this to configure.ac to generate
config.h since submodules are sharing the same file.

All checks needed are guaranteed, thus simply add it to the ending of file.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

configure.ac

@@ -273,6 +273,10 @@ AC_CHECK_LIB(socket, connect)
 dnl Checks for library functions.
 AC_CHECK_FUNCS([malloc memset socket])
 
+dnl Add define for libudns to enable IPv6 support
+dnl This is an option defined in the origin configure script
+AC_DEFINE([HAVE_IPv6], [1], [Enable IPv6 support in libudns])
+
 AM_COND_IF([USE_SYSTEM_SHARED_LIB],
   [],
   [AC_CONFIG_SUBDIRS([libsodium])])