Fix the is_eligible_for_constexpr test
Fix the is_eligible_for_constexpr test

Summary: `is_eligible_for_constexpr` caches the result which interferes with the test where types are created and destroyed in local scope so pointers may be recycled. Fix the issue by creating a new `is_eligible_for_constexpr` object every time.

Reviewed By: Mizuchi

Differential Revision: D27326911

fbshipit-source-id: c05c79498f6f542c6278c6d32c97dea4aad235a2

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