build-sys: enable timesyncd by default
timesync: always initialize structs when declaring them as far as possible with contsant values
timesync: use safe_close() where possible
sd-event: make it easy to bind signal handling to event loop exits

By passing a NULL callback provide a simple way to make event loops exit
on SIGTERM and other signals.
sd-event: allow disabling event sources when an event object is dying anyway
sd-resolve: make sure we can destroy a query object from its own callback handler
timesyncd: lookup name server via sd-resolve, support IPv6, react to SIGINT/SITERM