These were problematic but previously easy to miss. They're now
easy to spot thanks to build failures at Go tip as of CL 610736.

For golang/go#68796.

Change-Id: I167f2cce2376b4070460389c673d973e4521d3dc
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/610797
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>