macos: add support for targetting ARM64
macos: add support for targetting ARM64

Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/661>

nirbheek/cerbero,GStreamer/cerbero,GStreamer/cerbero,GStreamer/cerbero,nirbheek/cerbero,nirbheek/cerbero,nirbheek/cerbero,GStreamer/cerbero,GStreamer/cerbero