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: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

scripts/kconfig/conf.c

@@ -558,6 +558,7 @@ int main(int ac, char **av)
 		if (stat(".config", &tmpstat)) {
 			printf(_("***\n"
 				"*** You have not yet configured your kernel!\n"
+				"*** (missing kernel .config file)\n"
 				"***\n"
 				"*** Please run some configurator (e.g. \"make oldconfig\" or\n"
 				"*** \"make menuconfig\" or \"make xconfig\").\n"