this matches historical practice.

this matches historical practice.
(unlink_destination): New function, which checks for unlink failures.
(maybe_recoverable): Stay quiet if -U.
(extract_archive): Use O_EXCL if unlink_first_option.
Report unlink failures.
Use HAVE_SYMLINK, not S_ISLNK, to determine whether symlink exists.
Use HAVE_MKFIFO || defined mkfifo, not S_ISFIFO, to determine whether
mkfifo exists.