This commit adds code to setup.py to use ninja to manage
C++ and code generator dependencies rather than use raw setuptools.
This is based on similar code added to ONNX.
Enabled optionally when ninja is installed.
On my computer speed for a do-nothing build drops from 10s to 1.5 seconds.
Speed of other compilation steps is significantly improved as well.
Dependencies are tracked correctly so the need for ccache is reduced.
