Instead of abusing ALAST.

Passes GOARCH=mips64 toolstash -cmp.

Updates #14692.

Change-Id: Ie85e99cf76508c1d0f5847a4157056b614fd5cc6
Reviewed-on: https://go-review.googlesource.com/20341
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>