Fix C++20 build issues

Summary: Fix C++20 build issues

Reviewed By: ispeters

Differential Revision: D31842893

fbshipit-source-id: 64a4332939fd101b99ccba6f27c7df740a346844

folly/container/test/HeterogeneousAccessTest.cpp

@@ -203,7 +203,11 @@ Range<int const*> foo(small_vector<int, 2> const& sv) {
 
 TEST(HeterogeneousAccess, transparentMatches) {
   runTestMatches<std::string>("abcd");
+#if !defined(__cpp_lib_char8_t) || __cpp_lib_char8_t < 201907
   runTestMatches<std::string>(u8"abcd");
+#else
+  runTestMatches<std::u8string>(u8"abcd");
+#endif
   runTestMatches<std::wstring>(L"abcd");
   runTestMatches<std::u16string>(u"abcd");
   runTestMatches<std::u32string>(U"abcd");

folly/container/test/TrackingTypes.h

@@ -338,13 +338,14 @@ template <class T>
 class SwapTrackingAlloc {
  public:
   using Alloc = std::allocator<T>;
-  using value_type = typename Alloc::value_type;
-
-  using pointer = typename Alloc::pointer;
-  using const_pointer = typename Alloc::const_pointer;
-  using reference = typename Alloc::reference;
-  using const_reference = typename Alloc::const_reference;
-  using size_type = typename Alloc::size_type;
+  using AllocTraits = std::allocator_traits<Alloc>;
+  using value_type = typename AllocTraits::value_type;
+
+  using pointer = typename AllocTraits::pointer;
+  using const_pointer = typename AllocTraits::const_pointer;
+  using reference = value_type&;
+  using const_reference = value_type const&;
+  using size_type = typename AllocTraits::size_type;
 
   using propagate_on_container_swap = std::true_type;
   using propagate_on_container_copy_assignment = std::true_type;