On Win32 the setvbuf function requires the last parameter to be size between 2 and INT_MAX bytes, so the calls always failed. Since the whole point of the calls is to set line-buffered mode for the file handle and that's not supported on Win32 anyway, conditionally remove them.

Signed-off-by: Filip Navara <filip.navara@gmail.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>