cmd/compile/internal/logopt: occasional timeouts on netbsd-amd64-9_0 builders

[bcmills]

greplogs --dashboard -md -l -e 'panic: test timed out.*\n(?:\ngoroutine .*:\n(?:.+\n\t.+\n)+)*FAIL\s+cmd/compile/internal/logopt'

2021-12-10T19:26:50-766f89b/netbsd-amd64-9_0-n2
2021-04-15T00:40:43-566a87c/netbsd-amd64-9_0

Note that netbsd-amd64-9_0-n2 is one of the builders not believed to be affected by #49209.

(CC @bsiegert, @coypoop)

[bcmills]

As with #50138, a good starting point is probably to modify the test to terminate the process with SIGQUIT in case of a hang.

From https://build.golang.org/log/52da2ef801b2cf199641dab714931fe2cc1727ea, it appears that this test normally completes in under a second.