stderr is notable by its absence in the list of O_BINARY adjustments.

So -u does do 2/3 of what my windows_binary() does :)  Should I switch my test case to use stderr to demonstrate that it doesn't help with that?  I vaguely remember that early versions of DOS didn't do stderr, but I thought by the time Windows came along, let's see, was that about 1983?, that stderr was codified for DOS/Windows.  For sure it has never been missing in WinNT 4.0 +.