Lack of operator == in TEnumIterator

We want to enable the compile option `-D_GLIBCXX_DEBUG` to find potential bugs, but we meet compile errors: error_log.txt

Let's see the code in apache arrow project: https://github.com/apache/arrow/blob/984b59a2b4edb03479947c46007fc6142447f759/cpp/src/generated/parquet_types.cpp#L36

It constructs a std::map from a pair of iterators. However, in the debug mode of std::map (say, std::__debug::map), it will add additional check (such as boundary check) and need an operator == for these iterators.

So, I want to add an operator ==. 

Pull request: https://github.com/apache/thrift/pull/2633