when you're in a debianized tree, you should be building it with
`debian/rules binary' or `dpkg-buildpackage' as root, or read about
fakeroot.
> make[1]: *** No rule to make target `lookups/lookups.a', needed by `exim'. Stop.
> make[1]: Leaving directory `/home/elmer/exim/exim_3.12-10.1.deb/exim-3.12/build-Linux-i386'
> make: *** [go] Error 2
most likely you're missing something else as well. go in
build-*/lookups/, issue a `make' and watch that. it's supposed to give
you an error which will supposedly be more useful.