Fix more warnings

These were found attempting to enable -Werror

src/google/protobuf/arena_unittest.cc

@@ -1345,7 +1345,10 @@ TEST(ArenaTest, GetArenaShouldReturnNullForNonArenaCompatibleTypes) {
 
   // Test that GetArena returns nullptr for types that have a GetArena alias.
   struct {
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-local-typedef"
     using GetArena = Arena*;
+#pragma GCC diagnostic pop
   } has_get_arena_alias;
   EXPECT_EQ(nullptr, Arena::GetArena(&has_get_arena_alias));
 

src/google/protobuf/compiler/cpp/cpp_bootstrap_unittest.cc

@@ -131,7 +131,6 @@ class MockGeneratorContext : public GeneratorContext {
 
 const char kDescriptorParameter[] = "dllexport_decl=PROTOBUF_EXPORT";
 const char kPluginParameter[] = "dllexport_decl=PROTOC_EXPORT";
-const char kNormalParameter[] = "";
 
 const char* test_protos[][2] = {
     {"google/protobuf/descriptor", kDescriptorParameter},

src/google/protobuf/compiler/parser_unittest.cc

@@ -68,7 +68,7 @@ class MockErrorCollector : public io::ErrorCollector {
   std::string text_;
 
   // implements ErrorCollector ---------------------------------------
-  void AddError(int line, int column, const std::string& message) {
+  void AddError(int line, int column, const std::string& message) override {
     strings::SubstituteAndAppend(&text_, "$0:$1: $2\n", line, column, message);
   }
 };

src/google/protobuf/map_field_test.cc

@@ -78,25 +78,25 @@ class MapFieldBaseStub : public MapFieldBase {
   void SetRepeatedDirty() {
     state_.store(STATE_MODIFIED_REPEATED, std::memory_order_relaxed);
   }
-  bool ContainsMapKey(const MapKey& map_key) const { return false; }
-  bool InsertOrLookupMapValue(const MapKey& map_key, MapValueRef* val) {
+  bool ContainsMapKey(const MapKey& map_key) const override { return false; }
+  bool InsertOrLookupMapValue(const MapKey& map_key, MapValueRef* val) override {
     return false;
   }
-  bool DeleteMapValue(const MapKey& map_key) { return false; }
-  bool EqualIterator(const MapIterator& a, const MapIterator& b) const {
+  bool DeleteMapValue(const MapKey& map_key) override { return false; }
+  bool EqualIterator(const MapIterator& a, const MapIterator& b) const override {
     return false;
   }
-  int size() const { return 0; }
+  int size() const override { return 0; }
   void Clear() override {}
-  void MapBegin(MapIterator* map_iter) const {}
-  void MapEnd(MapIterator* map_iter) const {}
+  void MapBegin(MapIterator* map_iter) const override {}
+  void MapEnd(MapIterator* map_iter) const override {}
   void MergeFrom(const MapFieldBase& other) override {}
-  void Swap(MapFieldBase* other) {}
-  void InitializeIterator(MapIterator* map_iter) const {}
-  void DeleteIterator(MapIterator* map_iter) const {}
+  void Swap(MapFieldBase* other) override {}
+  void InitializeIterator(MapIterator* map_iter) const override {}
+  void DeleteIterator(MapIterator* map_iter) const override {}
   void CopyIterator(MapIterator* this_iterator,
-                    const MapIterator& other_iterator) const {}
-  void IncreaseIterator(MapIterator* map_iter) const {}
+                    const MapIterator& other_iterator) const override {}
+  void IncreaseIterator(MapIterator* map_iter) const override {}
   void SetDefaultMessageEntry(const Message* message) const {}
   const Message* GetDefaultMessageEntry() const { return NULL; }
 };

src/google/protobuf/testing/googletest.cc

@@ -119,7 +119,10 @@ string GetTemporaryDirectoryName() {
   // testing.  We cannot use tmpfile() or mkstemp() since we're creating a
   // directory.
   char b[L_tmpnam + 1];     // HPUX multithread return 0 if s is 0
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
   string result = tmpnam(b);
+#pragma GCC diagnostic pop
 #ifdef _WIN32
   // Avoid a trailing dot by changing it to an underscore. On Win32 the names of
   // files and directories can, but should not, end with dot.

src/google/protobuf/util/json_util_test.cc

@@ -58,8 +58,6 @@ using proto3::TestMessage;
 using proto3::TestOneof;
 using proto_util_converter::testing::MapIn;
 
-static const char kTypeUrlPrefix[] = "type.googleapis.com";
-
 // As functions defined in json_util.h are just thin wrappers around the
 // JSON conversion code in //net/proto2/util/converter, in this test we
 // only cover some very basic cases to make sure the wrappers have forwarded