GNU tar extraction can follow directory symlinks when overwrite semantics are enabled

During archive extraction, tar must avoid traversing attacker-controlled symlinks when creating or updating path components. In src/extract.c, directory creation and file-opening code paths use different fallbacks depending on platform support for O_NOFOLLOW and on overwrite/keep-directory-symlink options. This creates a symlink-following window in paths that should be treated as non-directory targets.