dnsdist: Add support for systemd-notify #3677
After pondering this, I feel there is no reason to generate a service file at all if there are no systemd(-dev) libraries installed, as the program is not intended to be run inside of systemd. We can stick a Type=simple service file in the contrib dir and have some documentation about this.
Imported https://github.com/mcgrof/funk-systemd/blob/b17396e7b1f5e93db74cae0e9123f39cf27a8339/src/m4/systemd.m4 as m4/systemd.m4 Imported https://github.com/mcgrof/funk-systemd/blob/b17396e7b1f5e93db74cae0e9123f39cf27a8339/src/m4/features.m4 as m4/ax_arg_default_enable_disable.m4
This patch is twofold: 1 - It detects the correct library for sd-daemon (either libsystemd-daemon (systemd pre-209) or libsystemd (systemd post-209) 2 - Detection of the library and files is only run once, even when systemd support detection is automatic (when using AX_AVAILABLE_SYSTEMD)