win32: Set unbuffered stdout

Win32 does not support line-buffering, but it allows
unbuffered output.

Unbuffered output is a good approximation. For typical output
statements which usually end with '\n', it's even identical.

Buffered output is unusable for program traces because of
its large delay.

Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>