Export of internal Abseil changes

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506fa3e10b3d8399ad937c32ecea26d1ad4e62bb by Abseil Team <absl-team@google.com>:

Disable ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE when GCC < 8.2.0 is used with libc++

PiperOrigin-RevId: 399707056

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656b7c7cee87f46a4bc7953618796f82da08e62c by Derek Mauro <dmauro@google.com>:

Remove the MSVC flag implementation from flag.h to help clarify that
methods on absl::Flag<T> are not part of the public API

PiperOrigin-RevId: 399584678

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a92a9bc156303bc663b84c4b704891ec8f67e333 by Abseil Team <absl-team@google.com>:

Get rid of MemcpyIfAllowed while continuing to suppress erroneous warnings

PiperOrigin-RevId: 399468864

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5f9a66895f707ba001fb51b88c0c6025f8c872a3 by Abseil Team <absl-team@google.com>:

Use feature testing to check for availability of invoke_result.

Feature testing should be available by C++20, which removes invoke_result.
https://en.cppreference.com/w/cpp/feature_test

PiperOrigin-RevId: 399447373

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946c0a502b4499dbfcabf1ab93ddde0048288fb4 by CJ Johnson <johnsoncj@google.com>:

Add rvalue-reference qualifier to the Commit method on ConstructionTransaction

PiperOrigin-RevId: 399442206

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726a4d036eff49aeb6fd0ca2b1775699b6844395 by Greg Falcon <gfalcon@google.com>:

Internal change

PiperOrigin-RevId: 399441870

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1df6d3f659b88dbac13c3d8e13db23bb3844ece2 by Abseil Team <absl-team@google.com>:

Clang-format whitespace changes

PiperOrigin-RevId: 399281271

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4a828cde95a07421d699ebac775b37810624214f by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 399234071

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e520c72b34ba2f98668c889139001f8276243d31 by Greg Falcon <gfalcon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 399233662
GitOrigin-RevId: 506fa3e10b3d8399ad937c32ecea26d1ad4e62bb
Change-Id: I92b9176d2387c08eb167f9268efa78b55b8e09c2

1 files changed, 1 insertions, 95 deletions

diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index 14209e7b..1a7e4d4d 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -71,101 +71,7 @@ ABSL_NAMESPACE_BEGIN
 template <typename T>
 using Flag = flags_internal::Flag<T>;
 #else
-// MSVC debug builds do not implement initialization with constexpr constructors
-// correctly. To work around this we add a level of indirection, so that the
-// class `absl::Flag` contains an `internal::Flag*` (instead of being an alias
-// to that class) and dynamically allocates an instance when necessary. We also
-// forward all calls to internal::Flag methods via trampoline methods. In this
-// setup the `absl::Flag` class does not have constructor and virtual methods,
-// all the data members are public and thus MSVC is able to initialize it at
-// link time. To deal with multiple threads accessing the flag for the first
-// time concurrently we use an atomic boolean indicating if flag object is
-// initialized. We also employ the double-checked locking pattern where the
-// second level of protection is a global Mutex, so if two threads attempt to
-// construct the flag concurrently only one wins.
-// This solution is based on a recomendation here:
-// https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html?childToView=648454#comment-648454
-
-namespace flags_internal {
-absl::Mutex* GetGlobalConstructionGuard();
-}  // namespace flags_internal
-
-template <typename T>
-class Flag {
- public:
-  // No constructor and destructor to ensure this is an aggregate type.
-  // Visual Studio 2015 still requires the constructor for class to be
-  // constexpr initializable.
-#if _MSC_VER <= 1900
-  constexpr Flag(const char* name, const char* filename,
-                 const flags_internal::HelpGenFunc help_gen,
-                 const flags_internal::FlagDfltGenFunc default_value_gen)
-      : name_(name),
-        filename_(filename),
-        help_gen_(help_gen),
-        default_value_gen_(default_value_gen),
-        inited_(false),
-        impl_(nullptr) {}
-#endif
-
-  flags_internal::Flag<T>& GetImpl() const {
-    if (!inited_.load(std::memory_order_acquire)) {
-      absl::MutexLock l(flags_internal::GetGlobalConstructionGuard());
-
-      if (inited_.load(std::memory_order_acquire)) {
-        return *impl_;
-      }
-
-      impl_ = new flags_internal::Flag<T>(
-          name_, filename_,
-          {flags_internal::FlagHelpMsg(help_gen_),
-           flags_internal::FlagHelpKind::kGenFunc},
-          {flags_internal::FlagDefaultSrc(default_value_gen_),
-           flags_internal::FlagDefaultKind::kGenFunc});
-      inited_.store(true, std::memory_order_release);
-    }
-
-    return *impl_;
-  }
-
-  // Public methods of `absl::Flag<T>` are NOT part of the Abseil Flags API.
-  // See https://abseil.io/docs/cpp/guides/flags
-  bool IsRetired() const { return GetImpl().IsRetired(); }
-  absl::string_view Name() const { return GetImpl().Name(); }
-  std::string Help() const { return GetImpl().Help(); }
-  bool IsModified() const { return GetImpl().IsModified(); }
-  bool IsSpecifiedOnCommandLine() const {
-    return GetImpl().IsSpecifiedOnCommandLine();
-  }
-  std::string Filename() const { return GetImpl().Filename(); }
-  std::string DefaultValue() const { return GetImpl().DefaultValue(); }
-  std::string CurrentValue() const { return GetImpl().CurrentValue(); }
-  template <typename U>
-  inline bool IsOfType() const {
-    return GetImpl().template IsOfType<U>();
-  }
-  T Get() const {
-    return flags_internal::FlagImplPeer::InvokeGet<T>(GetImpl());
-  }
-  void Set(const T& v) {
-    flags_internal::FlagImplPeer::InvokeSet(GetImpl(), v);
-  }
-  void InvokeCallback() { GetImpl().InvokeCallback(); }
-
-  const CommandLineFlag& Reflect() const {
-    return flags_internal::FlagImplPeer::InvokeReflect(GetImpl());
-  }
-
-  // The data members are logically private, but they need to be public for
-  // this to be an aggregate type.
-  const char* name_;
-  const char* filename_;
-  const flags_internal::HelpGenFunc help_gen_;
-  const flags_internal::FlagDfltGenFunc default_value_gen_;
-
-  mutable std::atomic<bool> inited_;
-  mutable flags_internal::Flag<T>* impl_;
-};
+#include "absl/flags/internal/flag_msvc.inc"
 #endif
 
 // GetFlag()