Revert "Revert "[libcxx] Put clang::trivial_abi on std::unique_ptr,...

Revert "Revert "[libcxx] Put clang::trivial_abi on std::unique_ptr, std::shared_ptr, and std::weak_ptr""

This reverts commit dc13ac02.

Rolling forward + fix typos and unused variables in tests

    Differential Revision: https://reviews.llvm.org/D82490