add @artifact_str

[rapus95]

when creating an artifact with julia 1.3 the BinaryBuilder pipeline drops everything in the right place such that I could depend on the newly created jll even for pre 1.3 packages. Thus, an artifact"dependency" which could be made via the recommended pre 1.3 solution using BinaryProvider.jl would be perfect and to my understanding in the scope of this package

[martinholters]

Closing as Compat now targets Julia 1.6 or later, where this is not needed anymore.