Make ColdClassTest work on ancient compilers
Make ColdClassTest work on ancient compilers

Summary:
Some older versions of GCC/glibc/etc do not have the
std::is_trivially*_constructible or std::is_trivially*_assignable traits.

Reviewed By: yfeldblum

Differential Revision: D6285887

fbshipit-source-id: 1eb4ae4f899dc1f528321f9f087390291687aca3

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