gentoo-overlay/net-dns/djbdns/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "https://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <use>
    <!-- leave this global flag defined here to avoid a pkgcheck warning -->
    <flag name="ipv6">
      Apply Fefe's patch (https://www.fefe.de/dns/) for ipv6 support.
    </flag>
  </use>
</pkgmetadata>