runtime: test failure with `segmentation fault` (and no other output) on `linux-ppc64le-buildlet`

[bcmills]

##### GOMAXPROCS=2 runtime -cpu=1,2,4 -quick
signal: segmentation fault (core dumped)
FAIL	runtime	20.337s

So far there is only one of these in the logs since CL 369751 — on linux-ppc64le-buildlet — but given the similarity to #49370 I wonder whether this may be a platform-independent bug in the test.
(CC @golang/runtime)

greplogs --dashboard -md -l -e 'signal: segmentation fault .*\nFAIL\s+runtime\s+' --since=2021-12-07

2022-03-10T01:28:37-9faef5a/linux-ppc64le-buildlet