packaging: handle systemd service detection

[patrick-stephens]

Resolves #7189 to ensure systemd services are included in appropriate packages.
Changes in #5818 seem to be triggeringpkg-config issues in the container builds for some targets so adding the old default as well.

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[patrick-stephens]

The macos test failures are unrelated, just a tweak to CI separately to enable them to fail.

[ptsneves]

I am fine with this PR. It tries to fallback. I checked that debian indeed does not ship systemd's original pkgconfig. I am investigating why but this is a good patch.

[patrick-stephens]

I am fine with this PR. It tries to fallback. I checked that debian indeed does not ship systemd's original pkgconfig. I am investigating why but this is a good patch.

My suspicion is we may need to use something like the --with-systemdsystemunitdir configure argument, I'm guessing something in the container definition is missing to provide the relevant information on Debian. However the priority for now was to get it working for the upcoming 2.1 release so just went simple.