+AC_ARG_ENABLE(ipv6-support,
+[ --disable-ipv6-support Disable IPv6 support and other RFC-2554-related improvements],
+[if test $enableval = yes; then
+ enable_ipv6_support=yes
+fi], enable_ipv6_support=yes)
+
+if test $enable_ipv6_support != yes; then
+ AC_MSG_WARN([Skipping checks for IPv6 support and other RFC-2554-related improvements.
+ Due to lock contention, this may result in slower DNS resolution for IPv4 setups, too.])
+elif test $target_type = mingw; then