Port distribution tarball to Solaris 10

Port distribution tarball to Solaris 10

* make-dist (taropt): Use 'tar -H ustar' to generate a portable
tar file format instead of a GNU-specific format.  Needed now that
Emacs tarballs contain file names longer than 100 bytes, e.g.:
emacs-28.1/test/lisp/gnus/mml-sec-resources/private-keys-v1.d/C072AF82DCCCB9A7F1B85FFA10B802DC4ED16703.key
emacs-28.1/test/lisp/emacs-lisp/bytecomp-resources/error-lexical-var-with-run-hook-with-args-until-success.el
Without this patch, extracting a tarball on Solaris 10 fails with
many diagnostics like “tar: ././@LongLink: typeflag 'L' not
recognized, converting to regular file”.