Read previousVersions for bincompat checking from a file (#3202) (#3208)

This makes it much easier to automate checking new versions as they are
released.

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Co-authored-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>
(cherry picked from commit 2c6028b0

)

Co-authored-by: Jack Koenig <koenig@sifive.com>