overload: Delete obsolete macros for undefining absl::Overload when C++ < 17

PiperOrigin-RevId: 726196763
Change-Id: Iccb643892f8b6ff4f6b456be0274e731f0dcd184

Author: dinord

absl/functional/overload.h

@@ -23,8 +23,6 @@
 // Before using this function, consider whether named function overloads would
 // be a better design.
 //
-// Note: absl::Overload requires C++17.
-//
 // Example:
 //
 //     std::variant<std::string, int32_t, int64_t> v(int32_t{1});
@@ -46,9 +44,6 @@
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 
-#if defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \
-    ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
-
 template <typename... T>
 struct Overload final : T... {
   using T::operator()...;
@@ -71,21 +66,6 @@ struct Overload final : T... {
 template <typename... T>
 Overload(T...) -> Overload<T...>;
 
-#else
-
-namespace functional_internal {
-template <typename T>
-constexpr bool kDependentFalse = false;
-}
-
-template <typename Dependent = int, typename... T>
-auto Overload(T&&...) {
-  static_assert(functional_internal::kDependentFalse<Dependent>,
-                "Overload is only usable with C++17 or above.");
-}
-
-#endif
-
 ABSL_NAMESPACE_END
 }  // namespace absl
 

absl/functional/overload_test.cc

@@ -18,16 +18,12 @@
 #include <string>
 #include <type_traits>
 
+#include "gtest/gtest.h"
 #include "absl/base/config.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/variant.h"
 
-#if defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \
-    ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
-
-#include "gtest/gtest.h"
-
 namespace {
 
 TEST(OverloadTest, DispatchConsidersTypeWithAutoFallback) {
@@ -209,5 +205,3 @@ TEST(OverloadTest, HasConstexprConstructor) {
 }
 
 }  // namespace
-
-#endif