configure: disable engines if OPENSSL_NO_ENGINE is defined

configure: disable engines if OPENSSL_NO_ENGINE is defined

Starting with LibreSSL 3.8.1 the engines have been removed which causes
the OpenVPN build to fail. This can be solved during configure by
checking if OPENSSL_NO_ENGINE is defined in opensslconf.h.

Signed-off-by: orbea <orbea@riseup.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230909134956.5902-1-orbea@riseup.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26994.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>