This matches SIGEMT on other systems that use it (SIGEMT is not used
for most linux systems).

Change-Id: If394c06c9ed1cb3ea2564385a8edfbed8b5566d1
Reviewed-on: https://go-review.googlesource.com/17874
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>