Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add reach-over include files to read i386/foo.h. In time, the pc98
specific code will migrate to these files to augment or replace the
version in i386/include and/or i386/linux. This should, in the
fullness of time, allow many of the #ifdef PC98 in the tree.

# These files are in the public domain because there is insufficient
# creative content in them. When you customize them, please add a
# copyright notice and license.

OK'd in principle by: nyan@