ukui-interface fails to cross build from source, because debian/rules
hard codes the build architecture qmake. There are two easy ways to get
the host architecture one. Using dh_auto_configure (and yeah you can
call this multiple times with different build systems) would be the
simplest. Using dpkg's buildtools.mk is the least invasive. I'm
attaching a patch of the latter approach for your convenience.

Helmut