If readline is not present, udftools fails to build. There is no configure switch — the relevant sources (wrudf.h, wrudf.c, wrudf-cmnd.c) rely on _GNU_SOURCE to determine whether readline is present.
should be all set now in the tree; thanks for the report! Commit message: Depend on readline since we use it http://sources.gentoo.org/sys-fs/udftools/udftools-1.0.0b-r9.ebuild?r1=1.5&r2=1.6