playerctl fails to cross build from source, because it fails running the
gtk-doc scanner. Fortunately, the documentation already has been
separated to an arch:all package, so running the gtk-doc scanner is no
longer necessary in arch-only builds such as cross builds. I'm attaching
a patch that skips gtk-doc in arch-only builds and verified that an
arch-only build produces the same .debs as a full build. Please consider
applying the patch as it makes playerctl cross buildable.

Helmut