If you compile enca while having recode installed, it will link against it. However this dependency is not express in the ebuild. In previous versions of enca the dependency was explicit in the ebuild, but it was taken out?
I think that it should have IUSE="recode" and depending on it build with or without librecode support. Alternatively it could always depend on app-text/recode like previous versions did but I doubt if recode functionality is really necessary.
Thanks for the report. A fix was committed yesterday for this problem, in which recode was made an explicit dependency.