84742cd867
[P2231R1](https://wg21.link/P2231R1) "Missing `constexpr` in `std::optional` and `std::variant`" was accepted as a C++20 Defect Report, not a C++17 Defect Report. Accordingly, `test_empty_emplace()` and `check_reset()` should be marked as `TEST_CONSTEXPR_CXX20`. Note that their `static_assert`s are properly guarded:4ce65423be/libcxx/test/std/utilities/optional/optional.object/optional.object.assign/emplace.pass.cpp (L270-L272)4ce65423be/libcxx/test/std/utilities/optional/optional.object/optional.object.mod/reset.pass.cpp (L53-L55)Found while running libc++'s tests with MSVC's STL, as we activate our `constexpr` here for C++20 and above.