Describe the bug

Even if I add --backport argparse to vermin, it still reports a minimum version requirement of Python 2.7.

To Reproduce

$ cat > foo.py
import argparse
$ vermin --backport argparse -vvvv foo.py
Detecting python files..
Analyzing using 4 processes..
2.7, 3.2     /Users/Adam/Downloads/foo.py
  L1 C7: 'argparse' requires 2.7, 3.2

Minimum required versions: 2.7, 3.2

Expected behavior

Any version of Python should work for this file.

Environment

• Vermin 0.10.4
• macOS 10.15.7
• Python 3.8.5

Additional information

If you have any trouble reproducing this, I suspect that this is a macOS + Python 3.8 bug. See https://docs.python.org/3.8/library/multiprocessing.html#contexts-and-start-methods:

Changed in version 3.8: On macOS, the spawn start method is now the default. The fork start method should be considered unsafe as it can lead to crashes of the subprocess. See bpo-33725.

One workaround would be to force it to always use the fork start method by replacing multiprocessing with multiprocessing.get_context('fork') everywhere it's used. We recently had to do this for Spack: spack/spack#18124

A more permanent workaround would be to ensure that both spawn and fork work as expected.