Check that polkit ITS rules are installed
Right now the build fails with the very non-obvious error message:
[25/498] Generating org.gnome.controlcenter.datetime.policy_panels@datetime_merge with a custom command.
FAILED: panels/datetime/org.gnome.controlcenter.datetime.policy
/usr/bin/meson --internal msgfmthelper ../panels/datetime/org.gnome.controlcenter.datetime.policy.in panels/datetime/org.gnome.controlcenter.datetime.policy xml /home/new/aports/testing/gnome-control-center/src/gnome-control-center-3.32.1/po
msgfmt: cannot locate ITS rules for ../panels/datetime/org.gnome.controlcenter.datetime.policy.in
ninja: build stopped: subcommand failed.
If polkit's ITS files aren't installed.