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/04-run-normal.tpkg/04-run-normal.dsc

@@ -0,0 +1,15 @@
+BaseName: 04-run-normal
+Version: 1.0
+Description: run drill and don't do anything fancy
+CreationDate: Tue Nov  1 14:59:25 CET 2005
+Maintainer: Miek Gieben
+Category: 
+Component:
+Depends: 
+Help: 04-run-normal.help
+Pre: 
+Post:
+Test: 04-run-normal.test
+AuxFiles: 
+Passed:
+Failure:

zonemaster-ldns/ldns/test/04-run-normal.tpkg/04-run-normal.help

@@ -0,0 +1 @@
+synopsis: tpkg -a <path of ldns> exe 04-run-normal

zonemaster-ldns/ldns/test/04-run-normal.tpkg/04-run-normal.test

@@ -0,0 +1,23 @@
+# #-- 03-run.test --#
+# 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:
+PATH=$PATH:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:.
+
+# first arg is the build dir
+TPKG_BUILD=$1
+
+cd $TPKG_BUILD
+cd drill/
+LD_LIBRARY_PATH="../.libs:$LD_LIBRARY_PATH" DYLD_LIBRARY_PATH="../.libs:$DYLD_LIBRARY_PATH" ./drill @k.root-servers.net mx miek.nl && \
+LD_LIBRARY_PATH="../.libs:$LD_LIBRARY_PATH" DYLD_LIBRARY_PATH="../.libs:$DYLD_LIBRARY_PATH" ./drill  mx miek.nl 
+if [[ $? -ne 0 ]]; then
+        exit 1
+fi
+
+LD_LIBRARY_PATH="../.libs:$LD_LIBRARY_PATH" DYLD_LIBRARY_PATH="../.libs:$DYLD_LIBRARY_PATH" ./drill @ mx miek.nl
+if [[ $? -ne 1 ]]; then
+        exit 1
+fi