I had a really quick look at it and it seems that something like
dh_auto_configure -- --enable-debug --with-qtlibdir=/usr/lib/$(shell dpkg-architecture -qDEB_HOST_MULTIARCH)
in debian/rules should be enough to get it built. The correct fix however is to use proper pkg-config macros in configure.ac and run autoreconf to regen the scripts.
I had a really quick look at it and it seems that something like
dh_auto_configure -- --enable-debug --with- qtlibdir= /usr/lib/ $(shell dpkg-architecture -qDEB_HOST_ MULTIARCH)
in debian/rules should be enough to get it built. The correct fix however is to use proper pkg-config macros in configure.ac and run autoreconf to regen the scripts.