Feature request: do not require a file Artifacts.toml if an override folder is used

[amontoison]

For libHSL, we use the folder src/override to provide the precompiled artifacts.
However, we still need to include a file Artifacts.toml in our HSL_jll.jl with valid download links even if the (dummy) artifacts are not used.

-> https://github.com/JuliaPackaging/JLLWrappers.jl/blob/master/src/toplevel_generators.jl#L135-L137