Cannot make sense of link error

[Nordlöw via Digitalmars-d-learn]

On Saturday, 9 September 2017 at 15:41:48 UTC, Nordlöw wrote:
> When I compile it separately I don't get the linker error.
>
> /usr/bin/dmd --version: DMD64 D Compiler v2.076.0-dirty
> /usr/bin/dub --version: DUB version 1.5.0, built on Sep  1 2017

Making the contents of the module zio.d empty has no effect...