Prepare for BoringSSL update.

This change tweaks things as needed so that the code will compile
against both the BoringSSL that's currently in Android and a version
from upstream. The BORINGSSL_201509 define is temporary to allow the
switch to happen without breaking the build and a followup change will
remove it.

Change-Id: Ie60d8fc4d88154feaca8ab5ea85645b78a85640f
1 file changed