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/build-solaris.sh

@@ -0,0 +1,50 @@
+#!/bin/ksh
+#
+# $Id$
+
+
+PREFIX=/opt/ldns
+OPENSSL=/usr/sfw
+SUDO=sudo
+
+MAKE_PROGRAM=gmake
+MAKE_ARGS="-j 4"
+
+OBJ32=obj32
+OBJ64=obj64
+
+SRCDIR=`pwd`
+
+
+test -d $OBJ32 && $SUDO rm -fr $OBJ32
+mkdir $OBJ32
+
+export CFLAGS=""
+export LDFLAGS="-L${OPENSSL}/lib -R${OPENSSL}/lib"
+
+(cd $OBJ32; \
+${SRCDIR}/configure --with-ssl=${OPENSSL} --prefix=${PREFIX} --libdir=${PREFIX}/lib; \
+$MAKE_PROGRAM $MAKE_ARGS)
+
+if [ `isainfo -k` = amd64 ]; then
+	test -d $OBJ64 && $SUDO rm -fr $OBJ64
+	mkdir $OBJ64
+
+	export CFLAGS="-m64"
+	export LDFLAGS="-L${OPENSSL}/lib/amd64 -R${OPENSSL}/lib/amd64"
+
+	(cd $OBJ64; \
+	${SRCDIR}/configure --with-ssl=${OPENSSL} --prefix=${PREFIX} --libdir=${PREFIX}/lib/amd64; \
+	$MAKE_PROGRAM $MAKE_ARGS)
+fi
+
+# optionally install
+#
+if [ x$1 = xinstall ]; then
+	(cd $OBJ32; $SUDO $MAKE_PROGRAM install-h)
+	(cd $OBJ32; $SUDO $MAKE_PROGRAM install-doc)
+	(cd $OBJ32; $SUDO $MAKE_PROGRAM install-lib)
+	if [ `isainfo -k` = amd64 ]; then
+		(cd $OBJ64; $SUDO $MAKE_PROGRAM install-lib)
+	fi
+fi