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: NSam Ravnborg <sam@ravnborg.org>

Makefile

@@ -477,18 +477,20 @@ ifeq ($(dot-config),1)
 
 # Read in dependencies to all Kconfig* files, make sure to run
 # oldconfig if changes are detected.
--include .config.cmd
+-include .kconfig.d
 
 include .config
 
 # If .config needs to be updated, it will be done via the dependency
 # that autoconf has on .config.
 # To avoid any implicit rule to kick in, define an empty command
-.config: ;
+.config .kconfig.d: ;
 
 # If .config is newer than include/linux/autoconf.h, someone tinkered
-# with it and forgot to run make oldconfig
-include/linux/autoconf.h: .config
+# with it and forgot to run make oldconfig.
+# If kconfig.d is missing then we are probarly in a cleaned tree so
+# we execute the config step to be sure to catch updated Kconfig files
+include/linux/autoconf.h: .kconfig.d .config
 	$(Q)mkdir -p include/linux
 	$(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig
 else

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;