MT#55283 add __ct to typed GList

This is a placeholder to keep the const-qualified type of the contained
type within the struct, so that it can be used via __typeof__ if
necessary.

Change-Id: Ib40c55daa2225b7f9a9a926a6fa74f9b1471b6de

lib/containers.h

@@ -162,7 +162,10 @@
 	union type_name##_list { \
 		GList l; \
 		struct { \
-			contained_type *data; \
+			union { \
+				contained_type *data; \
+				const contained_type *__ct; \
+			}; \
 			type_name##_list *next; \
 			type_name##_list *prev; \
 		}; \