Portage has noweb-2.9r6. Upstream doesn't have anything older than 2.10c, dated 17-Jul-2002. Most recent is 2-11b, dated 12-Jun-2006. The repository is http://www.eecs.harvard.edu/~nr/noweb/dist/ I downloaded the 2-11b source and it builds fine.
forgotten package... bumped now, thanks