Also, let's deflatten the lists of sources in preparation for the
next commit at the same time.
In systemctl, we split out systemctl-main.c to make sure the definition
of main() is in a separate object which allows us to extract the systemctl.c
object and link it in the fuzzer target without getting a multiple definition
error when linking.
This commit introduces a build-time option to enable/disable sysupdated
separately from sysupdate. 'auto' translated to enabled by default in
developer builds.
Optional features allow distros to define sets of transfers that can
be enabled or disabled by the system administrator. This is useful for
situations where a distro may want to ship some resources version-locked
to the core OS, but many people have no need for the resource, such as:
development tools/compilers, drivers for specialized hardware, language
packs, etc
We also rename sysupdate.d/*.conf -> sysupdate.d/*.transfer, because
now there are more than one type of definition in sysupdate.d/. For
backwards compat, we still load *.conf files as long as no *.transfer
files are found and the *.conf files don't try to declare themselves
as part of any features
Fixes https://github.com/systemd/systemd/issues/33343
Fixes https://github.com/systemd/systemd/issues/33344
While we are at it, replace the sloppy use of filename_is_valid() by the
less sloppy filename_part_is_valid() (as added by the preceeding
commit), since we don#t want to be too restrictive here. (After all,
version strings invalid as standalone filenames might be valid as part
of filenames, and hence we should allow them).