Well, I've pretty much answered my own question. I'm still not quite sure 
why the build died -- though my suspicion is that I actually ran out of swap 
space (since, before I had swap space, I got signal 11 deaths on packages 
when I ran out of RAM). 

As far as the shell dying, though, it's definitely a case of compatibility 
between the kernel and the program. It appears that, in some cases, if the 
kernel is newer than the program -- for example, I had a kernel compiled 
from release sources, and bash from Josh's 1.6F tarball -- the program can't 
handle it, and will coredump. I've fixed this issue by switching my default 
shell to /bin/sh, which built and installed OK, and then rebuilding bash. 

If anyone has any insight as to why this would occur, it'd be sincerely 
appreciated. Meanwhile, I think I'm going to try using the build.sh script 
to rebuild world, and hopefully be successful this time. 

Alex Kirk