loongson/pypi: links for backports-abc

INFO: Because this project isn't in the mirror_whitelist, no releases from root/pypi are included.

loongson/pypi backports_abc-0.5-py3-none-any.whl
loongson/pypi backports_abc-0.5-py2.py3-none-any.whl
loongson/pypi backports_abc-0.5-py2-none-any.whl