This seems to have broken arm64 in a mysterious way. Will try again later.

This reverts commit 0a3c991f.

Change-Id: Ic1b53413c4168977a27381d9cc6fb8d9d7cbb780
Reviewed-on: https://go-review.googlesource.com/12245Reviewed-by: Russ Cox <rsc@golang.org>