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

[Randy Bush]

> fresh csup, multiple amd64 machines
> 
> sh /usr/src/tools/install.sh -s -o root -g wheel -m 555   clang-tblgen /usr/obj/usr/src/tmp/legacy/usr/bin
> ===> gnu/usr.bin/gperf (obj,depend,all,install)
> /usr/obj/usr/src/tmp/usr/src/gnu/usr.bin/gperf created for /usr/src/gnu/usr.bin/gperf
> ===> gnu/usr.bin/gperf/doc (obj)
> /usr/obj/usr/src/tmp/usr/src/gnu/usr.bin/gperf/doc created for /usr/src/gnu/usr.bin/gperf/doc
> make: don't know how to make iterator.cc. Stop


sorry, that's RELENG_9