Fix buildinfo generation

Summary: Add the VCS and use the canonical revision.

Test Plan: arc package in both hg and git repos

Reviewers: wez

Reviewed By: wez

Differential Revision: https://phabricator.fb.com/D865662

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extra : rebase_source : caae0ded5ec3b258f02687861a571d1a8ceb8c1f
extra : amend_source : 52a087b6dfe7a52630a6578bd9f548bc74c14d6b