security/xmlsec1: Fix build with LibreSSL 2.7
- LibreSSL 2.7 implements most of OpenSSL 1.1 API
PR: D14851
Submitted by: Charlie Li <ml+freebsd vishwin info>
Approved by: maintainer time-out
Obtained from: https://github.com/lsh123/xmlsec/pull/167
Differential Revision: https://reviews.freebsd.org/D14851