MFC r354922

MFC r354922

> Author: imp <imp@ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f>
> Date:   Wed Nov 20 23:45:31 2019 +0000
>
>    Create /etc/os-release file.
>
>    Each boot, regenerate /var/run/os-release based on the currently running
>    system. Create a /etc/os-release symlink pointing to this file (so that this
>    doesn't create a new reason /etc can not be mounted read-only).
>
>    This is compatible with what other systems do and is what the sysutil/os-release
>    port attempted to do, but in an incomplete way. Linux, Solaris and DragonFly all
>    implement this natively as well. The complete standard can be found at
>    https://www.freedesktop.org/software/systemd/man/os-release.html
>
>    Moving this to the base solves both the non-standard location problem with the
>    port, as well as the lack of update of this file on system update.
>
>    Bump __FreeBSD_version to 1300060
>
>    PR: 238953
>    Differential Revision:  https://reviews.freebsd.org/D22271

Execpt bump __FreeBSD_version to 1201511