CL 151478 was suppose to fix the build failure on linux/arm64 but the
build constraint didn't exclude linux/arm64 properly.

Fixes #28982

Change-Id: Ia80265b0adba0384cd28bc2deb1726418664975a
Reviewed-on: https://go-review.googlesource.com/c/151303
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>