Add .cirrus.yml for FreeBSD build

Right now this is just a build test for FreeBSD, along with a Linux build
and "make check."  A later change will add "gmake check" for FreeBSD.

Signed-off-by: Ed Maste <emaste@freebsd.org>
Message-Id: <20191120211133.69281-1-emaste@freefall.freebsd.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

.cirrus.yml

@@ -0,0 +1,21 @@
+env:
+  CIRRUS_CLONE_DEPTH: 1
+
+freebsd_12_task:
+  freebsd_instance:
+    image: freebsd-12-1-release-amd64
+  install_script:
+    pkg install -y bison gmake pkgconf
+  build_script:
+    gmake
+
+linux_gcc_task:
+  container:
+    image: gcc:latest
+  install_script:
+    - apt-get update
+    - apt-get -y install bison flex
+  build_script:
+    - make
+  test_script:
+    - make check