I wrote:
> I see that the gcc farm[1] has another mips64 machine running Debian
> buster, so I've started a build there to see what happens.
Many kilowatt-hours later, I've entirely failed to reproduce this
on gcc230. Not sure how to investigate further. Given that your
original build machine is so slow, could it be timing-related?
Hard to see how, given the location of the crash, but ...
regards, tom lane