CI: add FreeBSD build with Cirrus CI

As a first step for automatic FreeBSD testing add a build and install
for FreeBSD versions 12.4, 13.2 and 14-snapshot using Cirrus CI.

Reviewed-by: Jose Luis Duran 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Martin Matuska <mm@FreeBSD.org>
Closes #15332

.cirrus.yml

@@ -0,0 +1,21 @@
+env:
+  CIRRUS_CLONE_DEPTH: 1
+  ARCH: amd64
+
+build_task:
+  matrix:
+    freebsd_instance:
+      image_family: freebsd-12-4
+    freebsd_instance:
+      image_family: freebsd-13-2
+    freebsd_instance:
+      image_family: freebsd-14-0-snap
+  prepare_script:
+    - pkg install -y autoconf automake libtool gettext-runtime gmake ksh93 py39-packaging py39-cffi py39-sysctl
+  configure_script:
+    - env MAKE=gmake ./autogen.sh
+    - env MAKE=gmake ./configure --with-config="user" --with-python=3.9
+  build_script:
+    - gmake -j `sysctl -n kern.smp.cpus`
+  install_script:
+    - gmake install

.gitignore

@@ -42,6 +42,7 @@
 !udev/**
 
 !.editorconfig
+!.cirrus.yml
 !.gitignore
 !.gitmodules
 !AUTHORS
@@ -60,7 +61,6 @@
 !TEST
 !zfs.release.in
 
-
 #
 # Normal rules
 #