Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

This patch contains a raw copy of unifdef.c
Next patch will modify it and add infrastructure to use it
Adding unifdef to the kernel is acked by the author.

The reason to add unifdef as part of the kernel source is that it is not
yet a common utility on most distributions.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>