For libsystemd's headers, the changes made depend on whether the
header is installed or not. For installed headers, the only change
made is that commonly included headers were moved to _sd-common.h.
For these headers, there should be no noticeable change in behavior
when including them. For non-installed headers, includes were replaced
with forward declarations where possible as usual.
Split out of #37344.
- drop unnecessary SYNTHETIC_ERRNO() when the logger does not propagate
error code,
- drop unnecessary '%m' in error message when the error code is
specified with SYNTHETIC_ERRNO(),
- add missing full stop at the end of log message,
- use RET_GATHER(),
- add missing ", ignoring.",
- upeercase the first letter, etc., etc...