mail-client/pinepgp-0.18.0-r1 requires pine. It will not build against alpine, which is a new replacement for pine (see bug 176904).
We don't support stuff that doesn't exist in the official tree.
http://bugs.gentoo.org/show_bug.cgi?id=229947 http://bugs.gentoo.org/show_bug.cgi?id=223935