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/masterdont/config_file.h

@@ -0,0 +1,61 @@
+/* confile_file.h - masterdont config file reading */
+
+#ifndef CONFIG_FILE_H
+#define CONFIG_FILE_H
+struct zones_t;
+
+#define DEFAULT_PORT    53 /* default is to use the DNS port */
+#define MAX_TCP         200 /* max number concurrent tcp queries */
+#define SERVER_BUFFER_SIZE 65535 /* bytes */
+#define TCP_LISTEN_BACKLOG 15 /* max number of waiting connections */
+#define TCP_PKT_SIZE    16384 /* bytes size max tcp packet */
+
+/** a config file that has been read in */
+struct config_file {
+	/** port number to use */
+	int port;
+};
+
+/** max number of nested include files */
+#define MAX_INCLUDES 100
+
+/** during config read */
+struct config_read {
+	/** the cfg file */
+	struct config_file* cfg;
+	/** zone tree */
+	struct zones_t* zones;
+
+	/** current include depth */
+	int include_depth;
+	/** stack of include files */
+	FILE* fstack[MAX_INCLUDES];
+	/** name of include files */
+	char* fnames[MAX_INCLUDES];
+	/** line number */
+	int lineno[MAX_INCLUDES];
+
+	/** is the temp zone entry filled out? */
+	int zone_read;
+	/** line number where we started reading this zone */
+	int zone_linenr;
+	/** zone entry we are reading */
+	char* zone_name;
+	/** zone dir */
+	char* zone_dir;
+};
+
+/** create structure with defaults */
+struct config_file* config_file_create(void);
+
+/** delete structure */
+void config_file_delete(struct config_file* cfg);
+
+/** read in a config file */
+void config_file_read(struct config_file* cfg, const char* fname,
+	struct zones_t* zones);
+
+/** during config read, add another zone */
+void config_file_add_zone(struct config_read* cr);
+
+#endif