dee cannot be cross built from source. There are several reasons. The
immediate problem is a failure to install the host architecture python3
interpreter. It really wants to run python3 during build, so a native
python3 needs to be used. This also applies to python3-gi, which is used
to discover the architecture-independent override directory.

Nextup, the gtk-doc scanner fails. Fortunately, dee separates the
documentation to an Arch:all package. Therefore, arch-only builds such
as cross builds may disable gtk-doc. Reproducible builds can be used to
verify the correctness of the change.

Last but not least, it performs a separate build during
override_dh_install. There, configure is invoked manually and thus
misses the crucial --host flag. Wrapping the invocation in
dh_auto_configure fixes this.

The attached patch combines the aforementioned suggestions and makes dee
cross buildable. Please consider applying it.

Helmut