Make it explicit that WIndows build requires UNICODE support

Make it explicit that WIndows build requires UNICODE support

The interactive service code implicitly treats TCHAR == WCHAR in
several places with the assumption that we build only with UNICODE
defined. Make this explicit and remove some redundant code.

Also replace openvpn_sntprintf(), _tprintf() and similar with
explicit wide string functions. This adds some definiteness as
to which stdio functions are used, and helps the next commit that
makes those calls C-standard compliant.

Also, replace direct swprintf calls with openvpn_swprintf.

Note: we need UNICODE defined mainly because of the use of
TEXT("..") throughout the code. If those are replaced by L"..",
we could build with just -municode as done for OpenVPN
core.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20210522033232.20548-1-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22437.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>