ck_stack: Add aliased attribute to ck_stack for GCC 4.4.

include/ck_stack.h

@@ -40,7 +40,7 @@ typedef struct ck_stack_entry ck_stack_entry_t;
 struct ck_stack {
 	struct ck_stack_entry *head;
 	char *generation CK_CC_PACKED;
-};
+} CK_CC_ALIASED;
 typedef struct ck_stack ck_stack_t;
 
 #define CK_STACK_INITIALIZER { NULL, NULL }