Fix "integer constant is too large for 'long' type" errors.

Change-Id: I018cdc805e19284b057a57d04c9665f0a35ccc3b
Signed-off-by: Piotr Sikora <piotr@cloudflare.com>
Reviewed-on: https://boringssl-review.googlesource.com/2040
Reviewed-by: Adam Langley <agl@google.com>