artiq-fast: add nativeBuildInputs to artiq-board-legacy.nix
artiq-board: fix scope of toPythonModule
artiq-board: use new --gateware-identifier-str
artiq-board: use legacy code for artiq<6
artiq-board: get/remove/re-add version identifiers
artiq-fast: build gateware from a self-contained separate source derivation
Addresses item 2. of Gitea issue #1.
Co-authored-by: Stephan Maka <stephan@spaceboyz.net>
Reviewed-on: #23
