Cannot create venv _without_ symlinks using Command Line Tools build of Python on macOS

[layday]

See https://bugs.python.org/issue38705. This seems to have bitten some users lately:

• Trouble following packaging libraries tutorial packaging-problems#493
• Trouble following packaging libraries tutorial: build fails inside virtualenv, missing License and Requires info for pip packaging-problems#488

Note that the venv CLI defaults to using symlinks on platforms other than Windows so we could do the same in build. We could otherwise discourage build users from relying on the macOS-provided Python.

[henryiii]

Using symlinks on Unix and following the default behavior of python -m venv <name> seems quite reasonable. Also saves a little space if anyone cares about a temporary venv. :)

[gaborbernat]

Does the issue also happen with virtualenv? Using virtualenv in these cases might also be a good workaround.

[henryiii]

That's the workaround we have been suggesting, yes. But it would be better to fix the problem if possible.