Bug#969534: ffc autopkg test failure

[Drew Parsons]

Source: ffc
Followup-For: Bug #969534
Control: forwarded -1 https://github.com/pypa/setuptools/issues/2295

Looks like setuptools is now deprecated upstream.

"python3 setup.py install --prefix <dir>" no longer installs an
importable module (site.py is no longer installed)

setuptools upstream recommends using pip instead to install packages
from source to non-system directories, see upstream issue #2295.