Regenerate Config.in when toys/*.c changes.
diff --git a/Makefile b/Makefile
index 0b284ff..ce35e33 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@
 include kconfig/Makefile
 
 $(KCONFIG_TOP): generated/Config.in
-generated/Config.in:
+generated/Config.in: toys/*.c
 	scripts/genconfig.sh
 
 HOSTCC:=cc