Check for polkit's ITS files during build
They're required for build:
[5/38] Compiling C++ object 'src/25a6634@@gnome-system-monitor@exe/load-graph.cp[6/38] Compiling C++ object 'src/25a6634@@gnome-system-monitor@exe/gsm_pkexec.cp[7/38] Generating org.gnome.gnome-system-monitor.policy__merge with a custom command.
FAILED: org.gnome.gnome-system-monitor.policy
/usr/bin/meson --internal msgfmthelper org.gnome.gnome-system-monitor.policy.in org.gnome.gnome-system-monitor.policy xml ../po
msgfmt: cannot locate ITS rules for org.gnome.gnome-system-monitor.policy.in