Add _multibuild support (linked package could be removed now)
https://openbuildservice.org/help/manuals/obs-reference-guide/cha.obs.multibuild.html#id-1.7.11.4 mentions that there is a build description file required for every flavor,
For smaller files there is also the option to use only one spec file for both flavors, but for bigger files this would make the spec file confusing.