[FreeBSD] Build Crystal app with Cirrus CI

.cirrus.yml

# https://cirrus-ci.com/task/4647371069980672
#
# Create static binary on FreeBSD
# Default FreeBSD's openssl = bug, build new version from source
#
# crystal + openssl + pkgconf = dependencies required to build.
# shards = package manager
# gmake = because I don't like standard Makefile
# Warning: When I try make std_spec compiler_spec on virtual machine with 2 threads of Ryzen5 1600 and 4gb ram, it killed my virtual machine.
#
# I will add auto-upload binary later
#
freebsd_instance:
  image_family: freebsd-12-1

task:
  install_script: pkg install -y crystal shards openssl pkgconf gmake
  script: shards install && git clone https://github.com/crystal-lang/crystal && cd crystal && gmake && cd .. && ./crystal/bin/crystal build src/Server.cr --release --static --no-debug