This ebuild has been forked from Gentoo Linux, primarily to implement the libgcrypt-compat ebuild. There was an ABI change between libgcrypt 1.5 and 1.6, meaning apps written for one may not work with the other.
Gentoo has an older version of libgcrypt that just installs a compatibility library, and uses a sub-slot to differentiate between the two.
I thought it best to have a separate ebuild called libgcrypt-compat for providing older versions of the libgcrypt shared library, and nothing else, specificially indended for binary package compatibility. Details can be found in Bug FL-1145.