Your package build depends on libxp-dev but does not declare this
relation in the debian/control file. This is currently not a problem as
this is pulled in by the lesstif2-dev package that you do depend on.
In the near future we'd like to replace lesstif2 in Debian with the
relicensed (open-)motif package. Lesstif2 was originally created as a
free alternative for motif, but in the meantime became unmaintained and
buggy. Motif itself is now free and got its latest maintenance release
To ease the transition that will happen sometime soon, we will follow
up on this, please explicitly build-depend on libxp-dev, as we don't
intend to include these depends in libmotif-dev.
Paul & Graham.
P.S. Debian is trying to get rid of libxp, but as long as your package
needs it, please declare explicitly.