It looks like doxygen is only needed for building the arch all lmdb-doc
package, so it could be moved from Build-Depends to Build-Depends-Indep.
While this is a pretty minor issue, I think it would be better and it
would at least allow lmdb to be built on archs which don't have doxygen
(currently only hurd-amd64, but it's been others in the past).

Scott K