libsystemd version >= 227 required when compiling --with-systemd

[stevenwinfield]

Hi,

Our production systems are currently running RHEL 7.8, where the version of libsystemd is 219.
However, the sd_listen_fds_with_names function was introduced in v227, a mere(!) five years ago:
systemd/systemd@8dd4c05

RHEL 7.8 was released in March this year, so there are likely to be a few others who are similarly affected:
https://access.redhat.com/articles/3078

This causes compile-time errors, whereas a configure-time check could catch this earlier.
Unless you wanted to switch to sd_listen_fds, which does exist in v219.

Thanks!