Terminal comma for FutexResult enumerators
Terminal comma for FutexResult enumerators

Summary: [Folly] Terminal comma for `FutexResult` enumerators. Style nit.

Reviewed By: meyering

Differential Revision: D6673523

fbshipit-source-id: abf9f4d3e99bf9a6d3042a49252b1b1190e69b9f

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