use cirrus-ci for FreeBSD builds

This fixes #265.

test/cirrus.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+# Copyright (c) 2007-2018 The OpenRC Authors.
+# See the Authors file at the top-level directory of this distribution and
+# https://github.com/OpenRC/openrc/blob/master/AUTHORS
+#
+# This file is part of OpenRC. It is subject to the license terms in
+# the LICENSE file found in the top-level directory of this
+# distribution and at https://github.com/OpenRC/openrc/blob/master/LICENSE
+# This file may not be copied, modified, propagated, or distributed
+# except according to the terms contained in the LICENSE file.
+
+set -e
+set -u
+set -x
+
+# These are steps to run on Cirrus CI under a jailed FreeBSD system.
+# See $TOP/.cirrus.yml for more info about the Cirrus CI setup.
+
+cpus=$(getconf NPROCESSORS_CONF || echo 1)
+gmake -j"${cpus}" -O
+gmake test