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/test/16-unit-tests-edns.tpkg/16-unit-tests-edns.pre

@@ -0,0 +1,45 @@
+# #-- 16-unit-tests-edns.pre--#
+# source the master var file when it's there
+[ -f ../.tpkg.var.master ] && source ../.tpkg.var.master
+# use .tpkg.var.test for in test variable passing
+[ -f .tpkg.var.test ] && source .tpkg.var.test
+# svnserve resets the path, you may need to adjust it, like this:
+export PATH=$PATH:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:.
+
+conf=`which autoconf` ||\
+conf=`which autoconf-2.59` ||\
+conf=`which autoconf-2.61` ||\
+conf=`which autoconf259`
+
+hdr=`which autoheader` ||\
+hdr=`which autoheader-2.59` ||\
+hdr=`which autoheader-2.61` ||\
+hdr=`which autoheader259`
+
+mk=`which gmake` ||\
+mk=`which make`
+
+echo "autoconf: $conf"
+echo "autoheader: $hdr"
+echo "make: $mk"
+
+opts=`../../config.status --config`
+echo options: $opts
+
+if [ ! $mk ] || [ ! $conf ] || [ ! $hdr ] ; then
+	echo "Error, one or more build tools not found, aborting"
+	exit 1
+fi;
+
+ssl=``
+if [[ "$OSTYPE" == "darwin"* && -d "/opt/homebrew/Cellar/openssl@1.1" ]]; then
+	ssl=/opt/homebrew/Cellar/openssl@1.1/1.1.1n/
+fi;
+
+#$conf 13-unit-tests-base.configure.ac > configure && \
+#chmod +x configure && \
+#$hdr 13-unit-tests-base.configure.ac &&\
+#eval ./configure --with-ldns=../../ with-ssl=$ssl "$opts" && \
+../../config.status --file 16-unit-tests-edns.Makefile
+$mk -f 16-unit-tests-edns.Makefile
+