memory_utils: make cleanup handler as unused

They are sometimes used to just clean something up automatically at end
of scope but the variables themselves might not be actually used.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/memory_utils.h

@@ -20,7 +20,8 @@
 			cleaner(*ptr);                   \
 	}
 
-#define call_cleaner(cleaner) __attribute__((__cleanup__(cleaner##_function)))
+#define call_cleaner(cleaner) \
+	__attribute__((__cleanup__(cleaner##_function))) __attribute__((unused))
 
 #define close_prot_errno_disarm(fd) \
 	if (fd >= 0) {              \