Log Message:
php-iconv: Overhaul iconv selection.

I noted a while back that this looked very wrong, and yes, it turns out to
be very wrong indeed, with over 70% of tests failing and php dumping core.

Simplify the selection so that the correct arguments are used for pkgsrc
libiconv as well as native iconv.  Remove confusing comments, and add the
correct TEST_TARGET while here.

Tested on SmartOS with pkgsrc libiconv, and on NetBSD and macOS with both
native iconv and pkgsrc libiconv.  It should be noted that pkgsrc libiconv
passes all tests, while both NetBSD and macOS native iconv have a number
of failures.

Bump PKGREVISION.