Add comment for the dummy macro compilation guard

Change-Id: I1da359df006f058c3e27a0d4bc91b50c4441a1da

Author: lumynou5

list.h

@@ -412,6 +412,7 @@ static inline void list_move_tail(struct list_head *node,
          &entry->member != (head);                                 \
          entry = list_entry(entry->member.next, typeof(*entry), member))
 #else
+// The negative width bit-field makes a compile-time error for use of this.
 #define list_for_each_entry(entry, head, member) \
     for (entry = (void *) 1; sizeof(struct { int : -1; }); ++(entry))
 #endif

scripts/checksums

@@ -1,3 +1,3 @@
 db6784ff3917888db4d1dceaa0570d99ed40e762  queue.h
-78828505183bf0444f574c0a33a4a1f5e3231994  list.h
+943e0653daa1d51c9f61d1652a644588af5969e2  list.h
 3bb0192cee08d165fd597a9f6fbb404533e28fcf  scripts/check-commitlog.sh