fix: populate ldns submodule and add autotools to LDNS build stage

- Re-cloned zonemaster-ldns with --recurse-submodules so the bundled
  ldns C library source (including Changelog and configure.ac) is present
- Added autoconf, automake, libtool to Dockerfile.backend ldns-build stage
  so libtoolize + autoreconf can generate ldns/configure during make

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-ldns/ldns/contrib/DNS-LDNS/lib/DNS/LDNS/DNSSecDataChain.pm

@@ -0,0 +1,87 @@
+package DNS::LDNS::DNSSecDataChain;
+
+use 5.008008;
+use strict;
+use warnings;
+
+use DNS::LDNS;
+
+our $VERSION = '0.61';
+
+sub rrset {
+    my $self = shift;
+    return DNS::LDNS::GC::own($self->_rrset, $self);
+}
+
+sub signatures {
+    my $self = shift;
+    return DNS::LDNS::GC::own($self->_signatures, $self);
+}
+
+sub parent {
+    my $self = shift;
+    return DNS::LDNS::GC::own($self->_parent, $self);
+}
+
+sub derive_trust_tree {
+    my ($self, $rr) = @_;
+
+    if (!DNS::LDNS::GC::is_owned($rr) or DNS::LDNS::GC::owner($rr) ne $self) {
+	die "The rr ($rr) must be in the data chain ($self)";
+    }
+    return DNS::LDNS::GC::own($self->_derive_trust_tree($rr), $self);
+}
+
+sub derive_trust_tree_time {
+    my ($self, $rr, $checktime) = @_;
+
+    if (!DNS::LDNS::GC::is_owned($rr) or DNS::LDNS::GC::owner($rr) ne $self) {
+	die "The rr ($rr) must be in the data chain ($self)";
+    }
+    return DNS::LDNS::GC::own(
+	$self->_derive_trust_tree_time($rr, $checktime), $self);
+}
+
+
+1;
+__END__
+
+=head1 NAME
+
+DNS::LDNS::DNSSecDataChain - DNSSec data chain element
+
+=head1 SYNOPSIS
+
+  use DNS::LDNS ':all'
+
+  chain = new DNS::LDNS::DNSSecDataChain
+  chain->print(fp)
+  chain->derive_trust_tree(rr)
+  chain->derive_trust_tree_time(rr, checktime)
+
+  # Node attributes
+  rrset = chain->rrset
+  rrset = chain->signatures
+  rrtype = chain->parent_type
+  pchain = chain->parent
+  rcode = chain->packet_rcode
+  rrtype = chain->packet_qtype
+  bool = chain->packet_nodata
+
+=head1 SEE ALSO
+
+http://www.nlnetlabs.nl/projects/ldns
+
+=head1 AUTHOR
+
+Erik Pihl Ostlyngen, E<lt>erik.ostlyngen@uninett.noE<gt>
+
+=head1 COPYRIGHT AND LICENSE
+
+Copyright (C) 2013 by UNINETT Norid AS
+
+This library is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself, either Perl version 5.14.2 or,
+at your option, any later version of Perl 5 you may have available.
+
+=cut