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.configure.ac

@@ -0,0 +1,96 @@
+#                                               -*- Autoconf -*-
+# Process this file with autoconf to produce a configure script.
+
+AC_PREREQ(2.57)
+AC_INIT(drill, 1.1.0, dns-team@nlnetlabs.nl, ldns-team)
+AC_CONFIG_SRCDIR([13-unit-tests-base.c])
+
+AC_AIX
+# Checks for programs.
+AC_PROG_CC
+AC_PROG_MAKE_SET
+
+# Checks for libraries.
+# Checks for header files.
+#AC_HEADER_STDC
+#AC_HEADER_SYS_WAIT
+# do the very minimum - we can always extend this
+AC_CHECK_HEADERS([getopt.h stdlib.h stdio.h assert.h netinet/in.hctype.h time.h])
+AC_CHECK_HEADERS(sys/param.h sys/mount.h,,,
+[
+  [
+   #if HAVE_SYS_PARAM_H
+   # include <sys/param.h>
+   #endif
+  ]
+])
+
+# ssl dir if needed
+AC_ARG_WITH(ssl, AC_HELP_STRING([--with-ssl=PATH], [set ssl library directory]),
+[
+	CPPFLAGS="$CPPFLAGS -I$withval/include"
+	LDFLAGS="$LDFLAGS -L$withval -L$withval/lib"
+])
+
+# check for ldns
+AC_ARG_WITH(ldns, 
+	AC_HELP_STRING([--with-ldns=PATH        specify prefix of path of ldns library to use])
+	,
+	[
+		specialldnsdir="$withval"
+		CPPFLAGS="$CPPFLAGS -I$withval/include"
+		LDFLAGS="$LDFLAGS -L$withval/lib"
+	]
+)
+
+AC_CHECK_LIB(ldns, ldns_rr_new,, [
+	AC_MSG_ERROR([Can't find ldns library])
+	]
+)
+
+AC_CHECK_HEADER(ldns/ldns.h,,  [
+	AC_MSG_ERROR([Can't find ldns headers])
+	]
+)
+
+AH_BOTTOM([
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <assert.h>
+
+#if STDC_HEADERS
+#include <stdlib.h>
+#include <stddef.h>
+#endif
+
+#ifdef HAVE_STDINT_H
+#include <stdint.h>
+#endif
+
+#ifdef HAVE_SYS_SOCKET_H
+#include <sys/socket.h>
+#endif
+
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h>
+#endif
+
+#ifdef HAVE_ARPA_INET_H
+#include <arpa/inet.h>
+#endif
+
+#ifdef HAVE_TIME_H
+#include <time.h>
+#endif
+])
+
+
+#AC_CHECK_FUNCS([mkdir rmdir strchr strrchr strstr])
+
+#AC_DEFINE_UNQUOTED(SYSCONFDIR, "$sysconfdir")
+
+AC_CONFIG_FILES([13-unit-tests-base.Makefile])
+AC_CONFIG_HEADER([config.h])
+AC_OUTPUT