buildworld: don't know how to make iterator.cc

[Randy Bush]

> Randy, when moving from one to another, are you deleting the contents
> of /usr/src before doing the csup?  More explicitly, this is what you
> should do when going from one release to another:
> 
> rm -fr /usr/src
> rm -fr /var/db/sup/src-all
> rm -fr /usr/obj/*
> csup ...

in a decade or more, i have never done the first two.  but i ain't proud
and will certainly try it now.

randy