Allow plugins to be skipped at runtime (#7691)

Allows plugins (such as carla) to be skipped when not installed

cmake/linux/apprun-hooks/carla-hook.sh

@@ -23,7 +23,8 @@ if command -v carla > /dev/null 2>&1; then
 		fi
 	done
 else
-	echo "[$ME] Carla does not appear to be installed.  That's OK, please ignore any related library errors." >&2
+	echo "[$ME] Carla does not appear to be installed, we'll remove it from the plugin listing." >&2
+	export "LMMS_EXCLUDE_PLUGINS=libcarla,${LMMS_EXCLUDE_PLUGINS}"
 fi
 
 # Additional workarounds for library conflicts