The distutils module from the standard library is deprecated and will
be removed in Python 3.12, and PEP 632 recommends using
distutils.ccompiler from setuptools, instead.
This code should eventually be rewritten to use zig-pypi, but for now
this suffices.
The `test_toolchain_cxx.py` tests on Gentoo definitely use compiler and
linker set with `_so_cxx`-suffixed executables. Tests use a proper
executable instead of `c++` after this change.
Signed-off-by: Adam Jeliński <ajelinski@antmicro.com>