autotools: fix configure with python >= 3.8

Would fail like this with python >= 3.8:

configure: checking for libraries required to embed python configure: error: Python libs not found. Windows requires Python modules to be explicitly linked to libpython.

Reason being that we must pass --embed now to python3-config to get the -lpython3.8 linker argument.

https://docs.python.org/dev/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build

Also see commit 22f28155 for Meson.