[master] add libns and remove liblwres

4708.   [cleanup]       Legacy Windows builds (i.e. for XP and earlier)
                        are no longer supported. [RT #45186]

4707.	[func]		The lightweight resolver daemon and library (lwresd
			and liblwres) have been removed. [RT #45186]

4706.	[func]		Code implementing name server query processing has
			been moved from bin/named to a new library "libns".
			Functions remaining in bin/named are now prefixed
			with "named_" rather than "ns_".  This will make it
			easier to write unit tests for name server code, or
			link name server functionality into new tools.
			[RT #45186]

lib/ns/lib.c

@@ -0,0 +1,102 @@
+/*
+ * Copyright (C) 2017  Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/*! \file */
+
+#include <config.h>
+
+#include <stddef.h>
+
+#include <isc/mem.h>
+#include <isc/msgcat.h>
+#include <isc/mutex.h>
+#include <isc/once.h>
+#include <isc/util.h>
+
+#include <dns/name.h>
+
+#include <ns/lib.h>
+
+
+/***
+ *** Globals
+ ***/
+
+LIBNS_EXTERNAL_DATA unsigned int			ns_pps = 0U;
+
+
+/***
+ *** Private
+ ***/
+
+static isc_once_t init_once = ISC_ONCE_INIT;
+static isc_mem_t *ns_g_mctx = NULL;
+static isc_boolean_t initialize_done = ISC_FALSE;
+static isc_mutex_t reflock;
+static unsigned int references = 0;
+
+static void
+initialize(void) {
+	isc_result_t result;
+
+	REQUIRE(initialize_done == ISC_FALSE);
+
+	result = isc_mem_create(0, 0, &ns_g_mctx);
+	if (result != ISC_R_SUCCESS)
+		return;
+
+	result = isc_mutex_init(&reflock);
+	if (result != ISC_R_SUCCESS)
+		goto cleanup_mctx;
+
+	initialize_done = ISC_TRUE;
+	return;
+
+  cleanup_mctx:
+	if (ns_g_mctx != NULL)
+		isc_mem_detach(&ns_g_mctx);
+}
+
+isc_result_t
+ns_lib_init(void) {
+	isc_result_t result;
+
+	/*
+	 * Since this routine is expected to be used by a normal application,
+	 * it should be better to return an error, instead of an emergency
+	 * abort, on any failure.
+	 */
+	result = isc_once_do(&init_once, initialize);
+	if (result != ISC_R_SUCCESS)
+		return (result);
+
+	if (!initialize_done)
+		return (ISC_R_FAILURE);
+
+	LOCK(&reflock);
+	references++;
+	UNLOCK(&reflock);
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+ns_lib_shutdown(void) {
+	isc_boolean_t cleanup_ok = ISC_FALSE;
+
+	LOCK(&reflock);
+	if (--references == 0)
+		cleanup_ok = ISC_TRUE;
+	UNLOCK(&reflock);
+
+	if (!cleanup_ok)
+		return;
+
+	if (ns_g_mctx != NULL)
+		isc_mem_detach(&ns_g_mctx);
+}