Unify build-system customization (Ardour/Mixbus)

tools/linux_packaging/build

@@ -187,6 +187,7 @@ Backends=$APPLIB/backends
 Themes=$Shared/themes
 Templates=$Shared/templates
 PluginMetadata=$Shared/plugin_metadata
+MixerSettings=$Shared/mixer_settings
 ExportFormats=$Shared/export
 Locale=$Shared/locale
 MidiMaps=$Shared/midi_maps
@@ -398,6 +399,12 @@ for x in $BUILD_ROOT/../osc/*.preset ; do
     cp "$x" $OSC
 done
 
+# Mixbus MixerSettings (if any)
+for x in $BUILD_ROOT/../mixer_settings/*.lua ; do
+    mkdir -p $MixerSettings  # create on demand
+    cp "$x" $MixerSettings
+done
+
 #Session templates
 cp -av $BUILD_ROOT/../templates $Templates