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/drill/drill_util.h

@@ -0,0 +1,65 @@
+/*
+ * util.h
+ * util.c header file 
+ * in ldns
+ * (c) 2005 NLnet Labs
+ *
+ * See the file LICENSE for the license
+ *
+ */
+
+#ifndef _DRILL_UTIL_H_
+#define _DRILL_UTIL_H_
+#include <ldns/ldns.h>
+
+
+/**
+ * Read  keys from filename and append to key_list.
+ */
+ldns_status read_key_file(const char *filename, ldns_rr_list *key_list,
+		bool silently);
+
+/**
+ * return a address rdf, either A or AAAA 
+ * NULL if anything goes wrong
+ */
+ldns_rdf * ldns_rdf_new_addr_frm_str(char *);
+
+/**
+ * print all the ds of the keys in the packet
+ */
+void print_ds_of_keys(ldns_pkt *p);
+
+/**
+ * print some rdfs of a signature
+ */
+void print_rrsig_abbr(FILE *fp, ldns_rr *sig);
+/**
+ * print some rdfs of a dnskey
+ */
+void print_dnskey_abbr(FILE *fp, ldns_rr *key);
+/**
+ * print some rdfs of a ds
+ */
+void print_ds_abbr(FILE *fp, ldns_rr *ds);
+
+/**
+ * print some rdfs of a rr in a rr_list
+ */
+void print_rr_list_abbr(FILE *fp, ldns_rr_list *sig, const char *usr);
+
+/**
+ * Alloc some memory, with error checking
+ */
+void *xmalloc(size_t s);
+
+/** 
+ * Realloc some memory, with error checking
+ */
+void *xrealloc(void *p, size_t s);
+
+/**
+ * Free the data
+ */
+void xfree(void *q);
+#endif /* _DRILL_UTIL_H_ */