Always build library object files with shared library cflags

This takes us away from the idea that we know exactly how our static
libraries are going to get used.  Instead, we make them available to
build shareable things with, be it other shared libraries or DSOs.

On the other hand, we also have greater control of when the shared
library cflags.  They will never be used with object files meant got
binaries, such as apps/openssl or test/test*.

With unified, we take this a bit further and prepare for having to
deal with extra cflags specifically to be used with DSOs (dynamic
engines), libraries and binaries (applications).

Reviewed-by: Rich Salz <rsalz@openssl.org>