Work around an MSVC expression SFINAE bug in DynamicParser
Work around an MSVC expression SFINAE bug in DynamicParser

Summary: The good news is that it's cleaner than it was to start with.

Reviewed By: yfeldblum

Differential Revision: D4215323

fbshipit-source-id: 6758092f1e76f60b360753026bb7716737a51304

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