The .orig.tar.gz is http://pike.ida.liu.se/pub/pike/latest-stable/Pike-v7.6.112.tar.gz, right?
I think we should do two things to begin with: 1) Apply the Debian-specific patches (debian/patches/*) at build time using dpatch or equivalent, and 2) clean up the clean target. I expect $(MAKE) distclean to restore everything to pre-build state, and it *almost* does. Two things are missing compared to the tarball: bin/pike and src/modules/Java/module.pmod.in. It's quite possible that those shouldn't have been in the tarball to begin with. After that I'm sure the install target can be simplified a lot too.