kbuild: be more explicit on missing .config file

Somewhat in reponse to kernel bugzilla #8197, be more explicit about
why 'make all' fails when there is no .config file.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
1 file changed