fix from Bernd Schmidt for realloc shrinkage bug

libc/stdlib/malloc/realloc.c

@@ -46,6 +46,11 @@ realloc (void *mem, size_t new_size)
      allocation unit (SIZE is already guaranteed to be so).*/
   new_size = HEAP_ADJUST_SIZE (new_size + MALLOC_HEADER_SIZE);
 
+  if (new_size < sizeof (struct heap_free_area))
+    /* Because we sometimes must use a freed block to hold a free-area node,
+       we must make sure that every allocated block can hold one.  */
+    new_size = HEAP_ADJUST_SIZE (sizeof (struct heap_free_area));
+
   MALLOC_DEBUG (1, "realloc: 0x%lx, %d (base = 0x%lx, total_size = %d)",
 		(long)mem, new_size, (long)base_mem, size);