Minimal changes to import IPython from IronPython

Summary:

1) `IPython/core/compilerop.py`: not all flags have the "compiler_flag" attribute

2) `IPython/core/completer.py`: `__main__` is undefined

3) `IPython/core/prompts.py`: `os.getuid()` is not defined

4) `IPython/lib/inputhook.py`: `ctypes` SystemError

5) `IPython/utils/process.py` and `IPython/utils/_process_cli.py`: adds a new `_process_cli.py` which would handle the processes under cli.

6) `IPython/utils/io.py`: opened devnull in append mode