Newer version of systemd-journald support the --relinquish and
--smart-relinquish options that enable cleaner handling of mounts at
shutdown as journald can be told to close any logging under
/var/log/journal so that the /var filesystem can be unmounted should it be
on a separate partition.

Backport this feature as it enables shutdown without failures, a highly
desirable trait in embedded products using systemd.

The significant changes from the upstream patches are:

* Including `util.h` rather than `errno-util.h`, as the functionality
  hasn't been split out into a separate header file in our version.
  https://gitlab.apertis.org/pkg/target/systemd/-/merge_requests/26/diffs#10b30dfe96faf3663f42076bdb4984ccdea14817_0_88
- Adding `ERRNO_IS_ACCEPT_AGAIN` to `varlink.c` (the header file it's
  expected to be in doesn't exist in our version)
  https://gitlab.apertis.org/pkg/target/systemd/-/merge_requests/26/diffs#10b30dfe96faf3663f42076bdb4984ccdea14817_0_93
- Working around the changed parameters for
  `JSON_VARIANT_OBJECT_FOREACH`, adding a call to
  `json_variant_string()`, based on how upstream was modified when the
  macro changed
  https://gitlab.apertis.org/pkg/target/systemd/-/merge_requests/26/diffs#10b30dfe96faf3663f42076bdb4984ccdea14817_0_772
- Expanding the code around `inotify_add_watch()` which got factored out
  to a function in newer versions of systemd
  https://gitlab.apertis.org/pkg/target/systemd/-/merge_requests/26/diffs#f4174ac09c9ebd5278fe22a02b6207223a00f92e_0_74



Signed-off-by: Martyn Welch <martyn.welch@collabora.com>