I forgot that the libc raise function only sends the signal to the
current thread.  We need to actually use kill and getpid here, as we
do on other systems.

Change-Id: Iac34af822c93468bf68cab8879db3ee20891caaf
Reviewed-on: https://go-review.googlesource.com/12704Reviewed-by: Russ Cox <rsc@golang.org>