Linux distros changed /var/run and /var/lock to reside on an tmpfs in
/run a long time ago, and buildroot seems to agree by providing this
tmpfs on all supported init systems.

Packages on the other hand are currently free to either use /var/run
or /run, and similarly using /var/lock should be identical to the
replacement /run/lock.

This series aims to ensure that *if* /var/lock is needed, then
it will be a symlink to /run/lock. Allowing packages to continue
working and allowing them to migrate to using /run/lock.

If all relevant packages are fixed,
the compatibility symlinks in /var can be dropped.

Status before this patch:

*   Systemd

    /run will be mounted by PID1, /var/run will be recreated by
    /usr/lib/tmpfiles.d/var.conf.

    Creating /run/lock/subsys and the compatibility symlink is handled
    in /usr/lib/tmpfiles.d/legacy.conf.
    But this is *currently not installed* by Buildroot, see [1].

*   OpenRC

    Seems to check for existence of a /run directory and does all
    necessary setup.

*   SysV

    /var/lock is currently a symlink to /tmp.

*   Busybox

    Same as sysv (Buildroot uses the sysv skeleton)

Note that we create /run/lock/subsys, so sysv scrips could expect this
directory to exist. Apart from simplifying scripts, creating the dir
early as root adds some security.

Signed-off-by: Norbert Lange <nolange79@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>