[SV 63867] Don't use --sort to generate error report tar files

[SV 63867] Don't use --sort to generate error report tar files

Older versions of GNU tar parse the TAR_OPTIONS variable, but do not
accept the --sort option: remove it before creating the error report
tar files.  Note we still require a modern GNU tar to create release
tar files.  Reported by Dmitry Goncharov <dgoncharov@users.sf.net>

* Makefile.am (check-regression): Remove --sort from TAR_OPTIONS