Furthermore, fread() has already handled EOF, so there's no need to do
it again. If we read a character, return it, otherwise return EOF.
Note that EOF means "EOF or error" here.
The "stddbg" stream was a cute idea but we never ended up using it in
practice, so let's simplify this and implement userspace dbgprintf() on top
of a simple dbgputch() syscall instead.
This makes debugging LibC startup a little bit easier. :^)
