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/codingstyle.tpkg/codingstyle.dsc

@@ -0,0 +1,16 @@
+BaseName: codingstyle
+Version: 1.0
+Description: Check LDNS CodingStyle
+CreationDate: Tue Mar 14 12:58:28 CET 2006
+Maintainer: Miek Gieben
+Category: 
+Component:
+CmdDepends: 
+Depends: 
+Help: codingstyle.help
+Pre: 
+Post: 
+Test: codingstyle.test
+AuxFiles: 
+Passed:
+Failure:

zonemaster-ldns/ldns/test/codingstyle.tpkg/codingstyle.help

@@ -0,0 +1 @@
+No arguments are used for this test

zonemaster-ldns/ldns/test/codingstyle.tpkg/codingstyle.test

@@ -0,0 +1,52 @@
+# #-- codingstyle.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=$PATH:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:.
+
+L=90
+OPT="-ncs -sai -nut -ce -nfca -nlp -ncdb -br -ts08 -i8 -nbad"
+
+LC_OSTYPE=$(echo $OSTYPE | tr 'A-Z' 'a-z')
+
+st=0
+for i in ../../*.c; do
+
+        case $i in
+        "../../util.c" | "../../host2str.c" | "../../resolver.c")
+                continue;;
+        "../../error.c" | "../../rr.c" | "../../str2host.c")
+                continue;;
+        "../../keys.c" | "../../linktest.c" | "../../dnssec.c")
+                continue;;
+        "../../packet.c" | "../../parse.c")
+                continue;;
+        esac
+
+        case $LC_OSTYPE in
+        linux*)
+                diff -w -u $i <(cat $i | indent -l$L $OPT) | grep ^---
+                ;;
+        *bsd*)
+                diff -w -u $i <(cat $i | gindent -l$L $OPT)| grep ^---
+                ;;
+        darwin*)
+		echo "Warning: Codingstyle not checked on osx"
+		exit 0
+                ;;
+        solaris*)
+		echo "Warning: Codingstyle not checked on solaris"
+		exit 0
+                ;;
+        esac
+              
+        if [[ $? -eq 1 ]]; then
+                st=1
+        fi
+done
+if [[ $st -eq 0 ]]; then
+        exit 1
+fi
+exit 0