Summary:
Currently the cpp_extension build in benchmarks is misleading as it has the same name with torch.utils.cpp_extension

Pull Request resolved: https://github.com/pytorch/pytorch/pull/58708

Test Plan:
Run from `./benchmarks/operator_benchmark/pt_extension` folder:
```
python setup.py install
python cpp_extension_test.py
```

Note: CI doesn't matter as currently benchmarks/ folder is not compiled/test against CI

Reviewed By: robieta

Differential Revision: D28585582

Pulled By: walterddr

fbshipit-source-id: fc071040cf3cb52ee6c9252b2c5a0c3043393f57