Summary: Model ` std::__optional_storage_base::has_value` as this is what we see in clang AST when translating `std::optional::has_value` for libc++. For libstdc++, we get `std::optional::has_value` as expected.
Reviewed By: skcho, jvillard
Differential Revision: D25585543
fbshipit-source-id: b8d9d2902