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/error.c

@@ -0,0 +1,86 @@
+/**
+ * error.c
+ *
+ * error reporting routines
+ * basically wrappers around printf
+ *
+ * (c) 2005 NLnet Labs
+ *
+ * See the file LICENSE for the license
+ *
+ */
+
+#include "drill.h"
+#include <ldns/ldns.h>
+
+static void
+warning_va_list(const char *fmt, va_list args)
+{
+        fprintf(stderr, "Warning: ");
+        vfprintf(stderr, fmt, args);
+        fprintf(stderr, "\n");
+}
+
+void
+warning(const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	warning_va_list(fmt, args);
+	va_end(args);
+}
+
+static void
+error_va_list(const char *fmt, va_list args)
+{
+        fprintf(stderr, "Error: ");
+        vfprintf(stderr, fmt, args);
+        fprintf(stderr, "\n");
+}
+
+void
+error(const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	error_va_list(fmt, args);
+	va_end(args);
+	exit(EXIT_FAILURE);
+}
+
+static void
+verbose_va_list(const char *fmt, va_list args)
+{
+        vfprintf(stdout, fmt, args);
+        fprintf(stdout, "\n");
+}
+
+/* print stuff */
+void
+mesg(const char *fmt, ...)
+{
+	va_list args;
+	if (verbosity == -1) {
+		return;
+	}
+	fprintf(stdout, ";; ");
+	va_start(args, fmt);
+	verbose_va_list(fmt, args);
+	va_end(args);
+}
+
+#if 0
+/* print stuff when in verbose mode (1) */
+void
+verbose(const char *fmt, ...)
+{
+	va_list args;
+	if (verbosity < 1) {
+		return;
+	}
+
+	va_start(args, fmt);
+	verbose_va_list(fmt, args);
+	va_end(args);
+}
+#endif