xbps-src: added new var 'system_groups' for pkgs requiring new system groups.

xbps-src/shutils/metadata_scripts.sh

@@ -92,6 +92,13 @@ _EOF
 		echo "export openrc_services=\"${openrc_services}\"" >> $tmpf
 	fi
 
+	#
+	# Handle system groups.
+	#
+	if [ -n "${system_groups}" ]; then
+		_add_trigger system-accounts
+		echo "export system_groups=\"${system_groups}\"" >> $tmpf
+	fi
 	#
 	# Handle system accounts.
 	#
@@ -118,7 +125,6 @@ _EOF
 			unset homedir shell descr groups
 		done
 	fi
-
 	#
 	# Handle GNU Info files.
 	#