libnih1.0.3-4ubuntu15 gained cross-build support which is great, but it has a couple of things wrong.
The first is simple and trivial to fix. A BUILD/HOST typo in configure. Which causes it to fail to find dbus-1, because it used the build-arch pkgconfig. This probably wasn't previously noticed due to the work-around decribed of installing both build-arch and host-arch build-deps.
The second is trickier. It tries to run tests using nih-dbus-tool, even is DEB_BUILD_OPTIONS=nocheck is set. These fail because nih-dbus-tool is the wrong arch. Oddly the rules file contains NIH_DBUS_TOOL=$(CURDIR)/build-dbus-tool/nih-dbus-tool/nih-dbus-tool, when cross-building, to carefully set this to use the version which has been built. This will of course not run unless qemu is available for the host arch (it isn't for arm64). It maybe that the above plus the dh_auto_configure -B build-dbus-tool/ --host=$(DEB_BUILD_GNU_TYPE) was intended to build this too for the build arch, but then the wrong-arch nih-dbus-tool file ends up in the nih-dbus-tool package, does it not? It would need to be built twice, once for each arch for this to work.
Ideally DEB_BUILD_OPTIONS=nocheck would simply stop these targets being run, and 'make all-am' instead of 'make all' seems to do this. I suspect that the tests aren't being run in fact, just built, but that fails because it uses this tool - not sure. I failed to discern exactly what the right rune for 'don't try to build/run the tests' is in dh_foo-speak, so instead elected to set NIH_DBUS_TOOL to use the build-arch tool. This works fine. Enforcing this build-dep needs a :native so can't be done for the time being, but I see the package already has some of those pending.
Finding the right rune to make DEB_BUILD_OPTIONS=nocheck skip this might be a better fix.