kconfig: introduce nonint_oldconfig and loose_nonint_oldconfig

This patch has been around for a long time in Fedora and Red Hat Enterprise
Linux kernels and it may be useful for others. The nonint_oldconfig target
will fail and print the unset config options while loose_nonint_oldconfig will
simply let the config option unset. They're useful in distro kernel packages
where the config files are built using a combination of smaller config files.

Arjan van de Ven wrote the initial nonint_config and Roland McGrath added the
loose_nonint_oldconfig.

Signed-off-by: Arjan van de Ven <arjan@redhat.com> [defunct email]
Whatevered-by: Kyle McMartin <kyle@redhat.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
[mmarek: whitespace fixes]
Signed-off-by: Michal Marek <mmarek@suse.cz>