Handle Debian's posix_local scheme

[stefanor]

The issue and solution is the same as OSX.
The venv scheme wasn't standardised yet, so it's not using it yet.

Fixes: https://bugs.debian.org/1009916

[henryiii]

Could probably duplicate this test and modify to cover this?

build/tests/test_env.py

Lines 50 to 56 in 0b40b40

	@pytest.mark.skipif(IS_PYPY3, reason='PyPy3 uses get path to create and provision venv')
	@pytest.mark.skipif(sys.platform != 'darwin', reason='workaround for Apple Python')
	def test_can_get_venv_paths_with_conflicting_default_scheme(mocker):
	get_scheme_names = mocker.patch('sysconfig.get_scheme_names', return_value=('osx_framework_library',))
	with build.env.IsolatedEnvBuilder():
	pass
	assert get_scheme_names.call_count == 1

[stefanor]

Yeah, can do. I saw that test.

It won't be deep enough to give you a failure, unless run directly on the system python on a Debian system, but better than nothing.

[stefanor]

It won't be deep enough to give you a failure, unless run directly on the system python on a Debian system, but better than nothing.

Actually, I think this (otherwise noop) mock can ensure a failure, there.

[stefanor]

Coverage shows as decreasing, but if the python knows about posix_local, it'll run the test and increase coverage.

[gaborbernat]