[guix] Deduplicate the tar options and sort the source package

Summary:
This makes the achive file ordering deterministic and the tar behavior
more consistent.

Test Plan:
Run twice:

./contrib/guix/guix-clean && ./contrib/guix/guix-build && cat output/**/SHA256SUMS.part

Check the hashes are the same.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15648