Copying/pickling regression in 0.14

[bocklund]

In PyCalphad, we have some tests that test deepcopying/pickling and our tests have been showing a regression for SymEngine 0.14 on Windows only across Python versions.

I haven't been able to come up with a pure SymEngine reproducer yet, but I've made some notes in an issue in the PyCalphad repo: pycalphad/pycalphad#601 if anyone has ideas on changes that could have caused this or what I can do to make a pure SymEngine reproducible example.

[isuruf]

There were changes to the pickling in the C++ library. If you can make a pure SymEngine reproducible example I can have a look