contrib/vcpkg-ports: add pkcs11-helper port

contrib/vcpkg-ports: add pkcs11-helper port

pkcs11-helper is a dependency library used by OpenVPN.
So far it has been built only by mingw.

Since we're making MSVC build system a first class citizen,
we need to build depencencies with MSVC, which we do with vcpkg.
All dependencies are in vcpkg official repo, expect pkcs11-helper.

This provides vcpkg port for building pkcs11-helper.

Example usage:

 vcpkg --overlay-ports=<openvpn>\contrib\vcpkg-ports install pkcs11-helper

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210607104213.216-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22503.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 36b9aa0c1e40f3e4bd021b2fbd2a479ef148bc90)