Faiss 1.7.1

Prepare for release v1.7.1. (#1915)

Summary: Pull Request resolved: https://github.com/facebookresearch/faiss/pull/1915

Reviewed By: mdouze

Differential Revision: D28749880

Pulled By: beauby

fbshipit-source-id: 4dcb0a5eac8f84d26570a0fb6f3e357bc2f1151c