qpxtool fails to cross build from source for quite a number of reasons.
The immediate failure is running the build architure qmake. Looking into
the configure script, it seems that one is supposed to pass --target for
cross builds and while that helps with not using the build architecture
compiler, it also messes up CC vs CXX. And then --target doesn't fix the
qmake invocation, so one also gets to pass --qmake. That gets quite a
bit further until strip fails. Stripping during build is a bad as it not
only breaks cross building but also generation of -dbgsym packages as
well as DEB_BUILD_OPTIONS=nostrip. To make matter worse, the upstream
build system offers little options between a full debug build and a
stripped release build, so I opted for supplying a non-stripping strip.
Things don't stop breaking here. Manual pages are still missing. Looking
through the log, I noticed lrelease silently failing. That latter is
caused by missing :native dependencies required for running lrelease,
but that doesn't fix the manual pages. Something is breaking the manual
page location as /usr/man rather than /usr/share/man during cross
builds. Instead of digging further, I just added --mandir. So after this
long journey I offer you this invasive patch. What do you think?

Also consider moving away from a handcrafted configure script towards a
more common build system such as qmake, cmake, meson or autoconf. All of
these tend to just work for cross building.

Helmut