Add support for FreeBSD AArch64 (#387)

* Add support for FreeBSD AArch64

* Restrict the libgfortran versions on FreeBSD AArch64

At the moment, we only have GCC 7+ on FreeBSD AArch64, which means we
only want `expand_gfortran_versions` to include libgfortran versions 4
and 5 on that platform.

* Update PlatformSupport version, add some tests

* filter in gcc_version

* Bump minor version for a release with new features

Author: ararslan