allocator: 'die' routine is now given requested size

allocator: 'die' routine is now given requested size

* lib/allocator.h (struct allocator.die): New size arg.
* lib/careadlinkat.c (careadlinkat): Pass size to 'die' function.
If the actual problem is an ssize_t limitation, not a size_t or
malloc failure, fail with errno==ENAMETOOLONG instead of calling 'die'.