Allow users to install converters/libiconv on 10.x systems if they
decided to build world with WITHOUT_ICONV set. There's no need for
this check to be based on OSVERSION.
Some users (i.e. me), report subtle application breakages with the
iconv-from-src that disappear when iconv-from-ports is installed.
Allow for a bridge till these issues are sorted out.
Approved by: portmgr (bdrewery)