It references a non-existent src-uri for an older version of tmpwatch. It also doesn't patch the source to reflect the fact that fuser is in /bin on gentoo rather than /sbin. I have attached a fixed ebuild. Not sure if my src-uri is the best one to use but it works.
Created attachment 13880 [details] Fixed ebuild for tmpwatch-2.8.4
Looks like I may have been premature in saying the src_uri was wrong. Someone else reported that it works fine now. Perhaps there was something up with the servers earilier. I was tired, sorry. Still, the ebuild does need to edit tmpwatch.c with the correct path to fuser.
The fuser thing is fixed in 2.9.0. Thanks for finding this!