Fixes warnings in https://github.com/google/oss-fuzz/issues/864#issuecomment-458596374

src/google/protobuf/arenastring.h

@@ -195,6 +195,8 @@ struct PROTOBUF_EXPORT ArenaStringPtr {
     this_ptr->swap(*other_ptr);
 #else
     std::swap(ptr_, other->ptr_);
+    (void)default_value;
+    (void)arena;
 #endif
   }
 

src/google/protobuf/util/field_comparator.h

@@ -182,7 +182,7 @@ class PROTOBUF_EXPORT DefaultFieldComparator : public FieldComparator {
   // basic types (instead of submessages). They return true on success. One
   // can use ResultFromBoolean() to convert that boolean to a ComparisonResult
   // value.
-  bool CompareBool(const FieldDescriptor& field, bool value_1, bool value_2) {
+  bool CompareBool(const FieldDescriptor& /* unused */, bool value_1, bool value_2) {
     return value_1 == value_2;
   }
 
@@ -199,27 +199,27 @@ class PROTOBUF_EXPORT DefaultFieldComparator : public FieldComparator {
   // CompareFloat.
   bool CompareFloat(const FieldDescriptor& field, float value_1, float value_2);
 
-  bool CompareInt32(const FieldDescriptor& field, int32 value_1,
+  bool CompareInt32(const FieldDescriptor& /* unused */, int32 value_1,
                     int32 value_2) {
     return value_1 == value_2;
   }
 
-  bool CompareInt64(const FieldDescriptor& field, int64 value_1,
+  bool CompareInt64(const FieldDescriptor& /* unused */, int64 value_1,
                     int64 value_2) {
     return value_1 == value_2;
   }
 
-  bool CompareString(const FieldDescriptor& field, const std::string& value_1,
+  bool CompareString(const FieldDescriptor& /* unused */, const std::string& value_1,
                      const std::string& value_2) {
     return value_1 == value_2;
   }
 
-  bool CompareUInt32(const FieldDescriptor& field, uint32 value_1,
+  bool CompareUInt32(const FieldDescriptor& /* unused */, uint32 value_1,
                      uint32 value_2) {
     return value_1 == value_2;
   }
 
-  bool CompareUInt64(const FieldDescriptor& field, uint64 value_1,
+  bool CompareUInt64(const FieldDescriptor& /* unused */, uint64 value_1,
                      uint64 value_2) {
     return value_1 == value_2;
   }