So to better illustrate the actual issue I'll be using an example from the python documentation [0][1].

Get the demo.c and the setup.py. Compile cpython first with --with-lto and then compile the demo.c with ./python3 setup.py build.

You will notice that various link time optimization linker flags are passed to the extension.

[0] https://docs.python.org/3/extending/extending.html#keyword-parameters-for-extension-functions
[1] https://docs.python.org/3/extending/building.html#building-c-and-c-extensions-with-distutils