Fix libdir path on darwin

Fix libdir path on darwin

In current Configure script, libdir can be specified either an absolute
path or relative, while in Configurations/shared-info.pl, on darwin
system "-install_name" only accepts relative libdir path, and the
program fails when receiving absolute libdir path. This PR is to fix
this and match requirements of scripts.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16393)