The immediate usefulness of this is in pterm.exe: when the user uses
-e to specify a command to run in the pterm, we retrieve the command
in Unicode, store it in CONF_remote_cmd as UTF-8, and then in conpty.c
we can extract it in the same form and convert it back to Unicode to
pass losslessly to CreateProcessW. So now non-ACP Unicode works in
that part of the pterm command line.