Unix build file template: symlink "simple" to "full" shlib selectively

Unix build file template: symlink "simple" to "full" shlib selectively

On Unix-like platforms where the shared library comes in a form with
and a form without SO version number, the one without is symbolically
linked to the one with.

However, we have Unix-like platforms where we don't deal with SO
version numbers, and where the "simple" shlib thereby ends up being
symbolically linked to itself.  A simple check of the two shlib file
names is enough to ensure that we only do the symbolic link when
actually necessary.

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14726)