legate.core: Non-editable install fails on MacOS, because sysconfig.get_platform() is misparsed

The install finishes right after all the files have been copied, with:

    File "/Users/mpapadakis/opt/miniconda3/envs/legate/lib/python3.9/site-packages/wheel/bdist_wheel.py", line 281, in get_tag
      plat_name = get_platform(self.bdist_dir)
    File "/Users/mpapadakis/opt/miniconda3/envs/legate/lib/python3.9/site-packages/wheel/bdist_wheel.py", line 52, in get_platform
      result = calculate_macosx_platform_tag(archive_root, result)
    File "/Users/mpapadakis/opt/miniconda3/envs/legate/lib/python3.9/site-packages/wheel/macosx_libfile.py", line 399, in calculate_macosx_platform_tag
      base_version = tuple(int(x) for x in base_version.split("."))
    File "/Users/mpapadakis/opt/miniconda3/envs/legate/lib/python3.9/site-packages/wheel/macosx_libfile.py", line 399, in <genexpr>
      base_version = tuple(int(x) for x in base_version.split("."))
  ValueError: invalid literal for int() with base 10: ''

I added some printfs around the failing operation (see them in context below), and it looks like at the final stage the sysconfig.get_platform() call returns “macosx–x86_64”, whereas in multiple occasions previously it had returned “macosx-10.9-x86_64”.

Full build log: https://gist.github.com/manopapad/57833f1e4a2932f2f3b4db72703bafb1