Mark the long overload of digits_to as noexcept
Mark the long overload of digits_to as noexcept

Summary: Well, the explicit instantion for it anyways. The extern template declaration for it declares it as `noexcept`, so MSVC generates an error because the explicit instantiation is not also marked as `noexcept`

Reviewed By: yfeldblum, ericniebler

Differential Revision: D3744090

fbshipit-source-id: 4e756b2761c23a436097a6131b9b2ecd59faf4f9

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