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/packaging/ldns-config.in

@@ -0,0 +1,47 @@
+#!/bin/sh
+
+prefix="@prefix@"
+exec_prefix="@exec_prefix@"
+VERSION="@PACKAGE_VERSION@"
+CFLAGS="@CFLAGS@"
+CPPFLAGS="@CPPFLAGS@ @LIBSSL_CPPFLAGS@"
+LDFLAGS="@LDFLAGS@ @LIBSSL_LDFLAGS@"
+PYTHON_CPPFLAGS="@PYTHON_CPPFLAGS@"
+PYTHON_LDFLAGS="@PYTHON_LDFLAGS@"
+LIBS="@LIBS@ @LIBSSL_LIBS@"
+LIBDIR="@libdir@"
+INCLUDEDIR="@includedir@"
+LIBVERSION="@VERSION_INFO@"
+
+
+for arg in $@
+do
+    if [ $arg = "--cflags" ]
+    then
+        echo "-I${INCLUDEDIR}"
+    fi
+    if [ $arg = "--python-cflags" ]
+    then
+        echo "${PYTHON_CPPFLAGS} -I${INCLUDEDIR}"
+    fi
+    if [ $arg = "--libs" ]
+    then
+        echo "${LDFLAGS} -L${LIBDIR} ${LIBS} -lldns"
+    fi
+    if [ $arg = "--python-libs" ]
+    then
+        echo "${LDFLAGS} ${PYTHON_LDFLAGS} -L${LIBDIR} ${LIBS} -lldns"
+    fi
+    if [ $arg = "-h" ] || [ $arg = "--help" ]
+    then
+        echo "Usage: $0 [--cflags] [--python-cflags] [--libs] [--python-libs] [--version]"
+    fi
+    if [ $arg = "--version" ]
+    then
+        echo "${VERSION}"
+    fi
+    if [ $arg = "--libversion" ]
+    then
+        echo "${LIBVERSION}"
+    fi
+done