kbuild: always run 'make silentoldconfig' when tree is cleaned

If the file .kconfig.d is missing then make sure to run
'make silentoldconfig', since we have no way to detect if
a Kconfig file has been updated.

-kconfig.d is created by kconfig and is removed as part
of 'make clean' so the situation is likely to occur in reality.

Jan Beulich <JBeulich@novell.com> reported this bug.

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

scripts/kconfig/util.c

@@ -33,7 +33,7 @@ int file_write_dep(const char *name)
 	FILE *out;
 
 	if (!name)
-		name = ".config.cmd";
+		name = ".kconfig.d";
 	out = fopen("..config.tmp", "w");
 	if (!out)
 		return 1;