The full library is a bit much, but this is enough to appease most of
cryptography.io.

Change-Id: I1bb0d83744c4550d5fe23c5c98cfd7e36b17fcc9
Reviewed-on: https://boringssl-review.googlesource.com/29365
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>