Attached trivial patch simply adds `(declare (debug ...))' to the
macro. I believe it is perfectly safe and trivial, no mention in NEWS
etc. is needed. I would ask to merge it to branch 26 if possible.

Note that it doesn't quite let you debug generators anyway because of
bug #28725, but the change makes sense regardless. In particular, with
`iter2' package you should be able to debug generator functions called
from `iter-do'.

Paul