Join the x509 and x509v3 directories

This has been long overdue.

Note that this does not join the X509 and X509V3 error modules, that
will be too many macro changes at this stage.

Fixes #8919

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8925)