With CUPS v2.3b5, the configuration directive `SetEnv`
moved from `cupsd.conf` to `cups-files.conf`.  See also
apple/cups@d47f6ae .

We have to follow up as `SetEnv` is now ignored in `cupsd.conf`.
Without this, executables called by cups
can't find other executables they depend on,
like `gs` or `perl`.

ccls: 0.20190301 -> 0.20190314.1

Actually, more like -> 8.5.0.1 as this version is made against the
branch with the pending fixup patch applied.

The problem with stacking chrootenv before was that CLONE_NEWUSER cannot
be used when a child uses chroot. So instead of that we use pivot_root
which replaces root in the whole namespace. This requires our new root
to be an actual fs so we mount tmpfs.

* Remove unused argument from pivot_root;
* Factor out tmpdir creation into a separate function;
* Remove unused fstype from bind mount;
* Use unlink instead of a treewalk to remove empty temporary directory.

To avoid symlink loops to /host in nested chrootenvs we need to remove
one level of indirection. This is also what's generally expected of
/host contents.

Save an option to log to file with new `logFile` option.

As a side effect deprecate `pidfile` option and instead use systemd's
RuntimeDirectory.

Support nested user chrootenv environments

firefoxPackages.tor-browser: 8.0.9 -> 8.5.0

datadog-agent: fix sha256 sum

nixos/printing: fix CUPS `SetEnv` directive placement