Add support for User Statically Defined Tracing (USDT) probes

This adds support for User Statically Defined Tracing (USDT).  On
Linux, this uses the header from SystemTap and dtrace utility, but the
support is universal as long as dtrace is available.

Also add the required infrastructure to add probes to libisc, libdns and
libns libraries, where most of the probes will be.

util/dtrace.sh

@@ -0,0 +1,49 @@
+#!/bin/sh
+
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# SPDX-License-Identifier: MPL-2.0
+#
+# 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 https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+USAGE="# Usage: ${0} [-h | -G] -s File.d [-o <File>]"
+
+mode=
+while getopts hGs:o: opt; do
+	case "${opt}" in
+		h) mode=header ;;
+		s) input=$OPTARG ;;
+		o) output=$OPTARG ;;
+		G) mode=object ;;
+		\?) echo $USAGE; exit 1;;
+	esac
+done
+shift $((OPTIND - 1))
+
+if test -z "${mode}" || test -z "${input}"; then
+	echo $USAGE; exit 1;
+fi
+
+case "${mode}" in
+	header)
+		if test -z "${output}"; then
+			output="$(basename "${input}" .d).h"
+		fi
+		PROVIDER=$(cat "${input}" | sed -ne 's/^provider \(.*\) {/\1/p' | tr "a-z" "A-Z")
+		sed -ne 's/.*probe \(.*\)(.*);/\1/p' "${input}" | tr "a-z" "A-Z" | while read PROBE; do
+			echo "#define ${PROVIDER}_${PROBE}_ENABLED() 0";
+			echo "#define ${PROVIDER}_${PROBE}(...)";
+		done > "${output}"
+		;;
+	object)
+		if test -z "${output}"; then
+			output="$(basename "${input}" .d).o"
+		fi
+		echo "extern int empty;" | gcc -xc -c - -fPIC -DPIC  -o "${output}"
+		;;
+esac