[3.7] bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733) by miss-islington · Pull Request #12734

[3.7] bpo-36565: Fix libregrtest for Python without builtin _abc (GH-12733) by miss-islington · Pull Request #12734 · python/cpython

…12733)

Fix reference hunting (``python3 -m test -R 3:3``) when Python has no
built-in abc module: fix _get_dump() reimplementation of libregrtest.
(cherry picked from commit 79b5d29)

Co-authored-by: Victor Stinner <vstinner@redhat.com>