libosinfo fails to cross build from source, because meson.build is
confused. It attempts to detect availability of gobject-introspection,
but decides that cross builds can never do gobject-introspection (even
though they now can on Debian). Then it enables vala support and fails,
because vala support requires gobject-introspection.

I suggest dropping the cross compilation condition. Once removing it,
the build proceeds much further until the gtk-doc scanner fails.
Ideally, the documentation would be separated to an arch:all -doc
package. Then, the -dev package would be much smaller and libosinfo
would become cross buildable.

In the mean time, I suggest fixing the confusion about
gobject-introspection.

Helmut