Bootstrap broken on i386-pc-mingw32

[François-Xavier Coudert]

> Yeah, it appears I was overly optimistic in hoping vsnprintf() would
> do what C99 says it does.  I do not have access to any system that
> shows the problem, but I've attached a patch that should fix it (it
> just reverts the oprintf() changes, which were not really necessary, I
> was just trying to be more efficient).

Thanks, that fixes it for me on i386-pc-mingw32.

FX