Require EC key support in Windows builds

Require EC key support in Windows builds

Do not support the use of OPENSSL_NO_EC on Windows.

We build Windows releases with EC key support enabled in
OpenSSL and there is no reason to disable it in OpenVPN.

TODO: If there are no platforms of interest where EC support
cannot be enabled in OpenSSL, we should make !defined(OPENSSL_NO_EC)
a general requirement.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20211019034118.28987-3-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22952.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>