gst-plugins-good 1.17.90 fails with -Dorc=enabled but no plugins using orc enabled

Since commit 31ff3287, meson configure fails with

meson.build:460:4: ERROR: alias_target takes at least 2 arguments. if orc is enabled, but neither audiofx, deinterlace, videobox nor videomixer are enabled.

The orc_targets array stays empty in this case, and so does the orc_update_targets array, which is the second argument to the failing array_target() call.

The problem can be worked around by either disabling orc, or enabling any of the plugins that use it.