To my surprise, r339376 successfully built both world and kernel,
then segfaulted in buildworld at about the 15MB mark in the logfile
on the final clean-start rebuild. 

The sequence was
svnlite up -r r339376
make cleandir
make cleandir
rm -rf /usr/obj/usr/
make -j4 -DNO_CLEAN kernel-toolchain
make -j4 -DNO_CLEAN buildkernel
make -j4 installkernel
shutdown -r now

make -j4 -DNO_CLEAN buildowrld

In this phase there was a segfault in cc at around the 15 MB point 
in the log file.

On a whim, the system was updated to r343731.