In order to make the transition to BoringSSL easier, this change links
opensslv.h to base.h. This allows code that currently includes
opensslv.h to continue to compile.

Change-Id: I7e77006745276f150f17fdc3e43240c71f3c02ef

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)