Enable DSO (Dynamic Shared Object) support. This makes it possible

Enable DSO (Dynamic Shared Object) support.  This makes it possible
for OpenSSL to load engines run-time, e.g. for using the opensc
engine port.

The OpenSSL Configure script enables DSO support on FreeBSD by
default, we just don't use the Configure script during OpenSSL builds
in the base system.

This is committed to -CURRENT now (before OpenSSL 0.9.8b import), so
it can be tested at bit in -CURRENT before being MFC'ed to 6-STABLE.

Prodded by:	ale
PR:		bin/79570
MFC after:	1 week