Fix .gitignore complaining about name collisions in subdirectories.

.gitignore

@@ -1,10 +1,10 @@
 syntax: glob
-.config*
-.single*
-change/
-generated/
-kconfig/mconf
-kconfig/conf
-kconfig/*.c
-toybox
-toybox_unstripped
+/.config*
+/.single*
+/change/
+/generated/
+/kconfig/mconf
+/kconfig/conf
+/kconfig/*.c
+/toybox
+/toybox_unstripped