how can I see g++ compile flags during build using setup.py?

Question

When I build Python API for dlib (dlib.net), I do python setup.py.
Dlib uses pybind11 for this. (and setup.py uses setuptools)
It uses cmake and builds ok, and I know eventually it is using g++ in my system.
For a simple test, I want to see what g++ compile options (like include, libraries) are being used.
How can I see them?