Build Fails for 8.1.1 with Python 3.7 Wrapping

Building VTK 8.1.1 with VTK_WRAP_PYTHON=ON fails with the following error:

VTK-8.1.1/Wrapping/PythonCore/vtkPythonArgs.cxx:105:9: error: assigning to 'char *' from incompatible type 'const char *'
    a = PyUnicode_AsUTF8(o);
        ^~~~~~~~~~~~~~~~~~~
VTK-8.1.1/Wrapping/PythonCore/vtkPythonArgs.cxx:311:11: note: in
      instantiation of function template specialization 'vtkPythonGetStringValue<char>' requested here
          vtkPythonGetStringValue(o, a, "string or None required"));
          ^

Changing line 105 in vtkPythonArgs.cxx to

a = const_cast<char*>(PyUnicode_AsUTF8(o));

removes the error.

I am using MacOS 10.13.5 with Clang 9.1.0.

Update: it is most likely related to the new const return type of PyUnicode_AsUTF8 in python 3.7 rather than the VTK version.