OPTIONS_DEFINE. This policy has been implemented only recently that's why we
have many ports violating this policy.
This patch adds the default options specified in the Porter's Handbook to
OPTIONS_DEFINE where they are being used. Ports maintained by
gnome@FreeBSD.org, kde@FreeBSD.org and x11@FreeBSD.org have been excluded.
Approved by: portmgr (bapt)
It's value is "--with-libiconv-prefix=/usr/local" for systems
before 100043 with ports libiconv and to use at systems post
100043 with base iconv it's value is "" (NULL).
Co-authors: bapt, madpilot and bsam (me)
