Use `if constexpr` instead of `absl::utility_internal::IfConstexprElseIfConstexprElse`

PiperOrigin-RevId: 728737911

src/google/protobuf/arena.h

@@ -32,7 +32,6 @@ using type_info = ::type_info;
 #include "absl/base/optimization.h"
 #include "absl/base/prefetch.h"
 #include "absl/log/absl_check.h"
-#include "absl/utility/internal/if_constexpr.h"
 #include "google/protobuf/arena_align.h"
 #include "google/protobuf/arena_allocation_policy.h"
 #include "google/protobuf/port.h"
@@ -195,12 +194,8 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
   // otherwise, returns a heap-allocated object.
   template <typename T, typename... Args>
   PROTOBUF_NDEBUG_INLINE static T* Create(Arena* arena, Args&&... args) {
-    return absl::utility_internal::IfConstexprElse<
+    if constexpr (is_arena_constructable<T>::value) {
-        is_arena_constructable<T>::value>(
-        // Arena-constructable
-        [arena](auto&&... args) {
       using Type = std::remove_const_t<T>;
-#ifdef __cpp_if_constexpr
       // DefaultConstruct/CopyConstruct are optimized for messages, which
       // are both arena constructible and destructor skippable and they
       // assume much. Don't use these functions unless the invariants
@@ -217,19 +212,13 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
           return static_cast<Type*>(CopyConstruct<Type>(arena, &args...));
         }
       }
-#endif
+      return CreateArenaCompatible<Type>(arena, std::forward<Args>(args)...);
-          return CreateArenaCompatible<Type>(arena,
+    } else {
-                                             std::forward<Args>(args)...);
-        },
-        // Non arena-constructable
-        [arena](auto&&... args) {
       if (ABSL_PREDICT_FALSE(arena == nullptr)) {
         return new T(std::forward<Args>(args)...);
       }
-          return new (arena->AllocateInternal<T>())
+      return new (arena->AllocateInternal<T>()) T(std::forward<Args>(args)...);
-              T(std::forward<Args>(args)...);
+    }
-        },
-        std::forward<Args>(args)...);
   }
 
   // API to delete any objects not on an arena.  This can be used to safely