Select linux/arm64 for the asm test.

Disable the cgo test for now.
Will fix properly in a follow-up.
Filed Issue 28829 to track it.

Updates #28829

Change-Id: Ic05f619700b06e91c43f8c150b089b8e77d92c85
Reviewed-on: https://go-review.googlesource.com/c/149937
Run-TryBot: Alan Donovan <adonovan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>