Fix format errors when cross-compiling for Windows

Fix format errors when cross-compiling for Windows

Not all supported windows formatting libs are C99 compliant and some do not
grasp %ll (similar to %zu).  Use int64_t and PRIi64 to work around that.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <1518788739-16610-1-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg16478.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>