cirrus: Added FreeBSD builds using Cirrus CI.

The build logs will be at https://cirrus-ci.com/github/curl/curl

Some tests are currently failing and so disabled for now. The SSH server
isn't starting for the SSH tests due to unsupported options used in its
config file. The DICT server also is failing on startup.

.cirrus.yml

@@ -0,0 +1,32 @@
+# Cirrus CI configuration
+# https://cirrus-ci.com/github/curl/curl
+
+task:
+  name: FreeBSD
+  freebsd_instance:
+    matrix:
+      image: freebsd-12-0-release-amd64
+      image: freebsd-11-2-release-amd64
+      image: freebsd-10-4-release-amd64
+
+  env:
+    CIRRUS_CLONE_DEPTH: 1
+    MAKE_FLAGS: -j 2
+
+  pkginstall_script:
+    - pkg install -y autoconf automake libtool pkgconf brotli openldap-client heimdal libpsl libmetalink libssh2 openssh-portable libidn2 librtmp libnghttp2 nghttp2 stunnel
+    - pkg delete -y curl
+  configure_script:
+    - ./buildconf
+    - ./configure --prefix="${HOME}"/install --enable-debug --with-libssh2 --with-brotli --with-gssapi --with-libidn2 --enable-manual --enable-ldap --enable-ldaps --with-librtmp --with-libmetalink --with-libpsl --with-nghttp2 || { tail -300 config.log; false; }
+  compile_script:
+    - make V=1
+  test_script:
+    # Some tests won't run if run as root so run them as another user.
+    # Make directories world writable so the test step can write wherever it needs.
+    - find . -type d -exec chmod 777 {} \;
+    # TODO: A number of tests are failing on FreeBSD and so are disabled.
+    # This should be investigated.
+    - sudo -u nobody make V=1 TFLAGS='-n -a -p !flaky !303 !304 !310 !311 !312 !313 !323 !504 !1082 !1242 !1243 !2002 !2003 !2034 !2035 !2037 !2038 !2041 !2042 !2048 !3000 !3001' test-nonflaky
+  install_script:
+    - make V=1 install

README.md

@@ -4,6 +4,7 @@
 [![Coverity passed](https://scan.coverity.com/projects/curl/badge.svg)](https://scan.coverity.com/projects/curl)
 [![Travis-CI Build Status](https://travis-ci.org/curl/curl.svg?branch=master)](https://travis-ci.org/curl/curl)
 [![AppVeyor Build Status](https://ci.appveyor.com/api/projects/status/l1vv31029huhf4g4?svg=true)](https://ci.appveyor.com/project/curlorg/curl)
+[![Cirrus Build Status](https://api.cirrus-ci.com/github/curl/curl.svg?branch=master)](https://cirrus-ci.com/github/curl/curl)
 [![Coverage Status](https://coveralls.io/repos/github/curl/curl/badge.svg)](https://coveralls.io/github/curl/curl)
 [![Backers on Open Collective](https://opencollective.com/curl/backers/badge.svg)](#backers)
 [![Sponsors on Open Collective](https://opencollective.com/curl/sponsors/badge.svg)](#sponsors)