Summary: Check in a simple auto-build manfiest so that developers can issue ad-hoc build for Windows in Appveyor.
Test Plan: Run it in test branch test_appveyor and it works well.
Reviewers: kradhakrishnan, rven, anthony, IslamAbdelRahman, yhchiang
Reviewed By: yhchiang
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D43839
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