build: Don't trash the .config file when src/Kconfig changes.

Revision 5325e91e introduced a change to force the rebuild of the
.config file when the src/Kconfig (or vgasrc/Kconfig) file changes.
However, this was causing a complete rebuild of the user's .config
file which would throw away the user's current settings.

On a rebuild, use the kbuild olddefconfig rule instead of defconfig to
attempt to keep the user's current settings.

Signed-off-by: Kevin O'Connor <>
diff --git a/Makefile b/Makefile
index cb15217..aba8a62 100644
--- a/Makefile
+++ b/Makefile
@@ -260,7 +260,7 @@
 $(OUT)autoconf.h : $(KCONFIG_CONFIG) ; $(call do-kconfig, silentoldconfig)
-$(KCONFIG_CONFIG): src/Kconfig vgasrc/Kconfig ; $(call do-kconfig, defconfig)
+$(KCONFIG_CONFIG): src/Kconfig vgasrc/Kconfig ; $(call do-kconfig, olddefconfig)
 %onfig: ; $(call do-kconfig, $@)
 help: ; $(call do-kconfig, $@)