The __cxx11 superficially looks related to the C++ ABI switch in gcc 5. You could either try to compile both PyTorch from source and your extension with the same compiler or share which version you used for your extension.
If you have a very recent cuda, gcc 6 is a great choice, I have used gcc 5 successfully since PyTorch 0.1.2, but I always self-compiled so I didn’t have consistency issues.
Best regards
Thomas