pyproject.toml: add "setuptools>=40.8.0"

[blueyed]

Fixes:

% pip install ~v/setuptools
Looking in indexes: http://localhost:3141/root/pypi/+simple/
Processing …/Vcs/setuptools
  Installing build dependencies ... done
  WARNING: Missing build requirements in pyproject.toml for file://…/Vcs/setuptools.
  WARNING: The project does not specify a build backend, and pip cannot fall back to setuptools without 'setuptools>=40.8.0'.
  Getting requirements to build wheel ... done
ERROR: Exception:
Traceback (most recent call last):
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/cli/base_command.py", line 153, in _main
    status = self.run(options, args)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/commands/install.py", line 382, in run
    resolver.resolve(requirement_set)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/legacy_resolve.py", line 201, in resolve
    self._resolve_one(requirement_set, req)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/legacy_resolve.py", line 365, in _resolve_one
    abstract_dist = self._get_abstract_dist_for(req_to_install)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/legacy_resolve.py", line 312, in _get_abstract_dist_for
    abstract_dist = self.preparer.prepare_linked_requirement(
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/operations/prepare.py", line 223, in prepare_linked_requirement
    abstract_dist = _get_prepared_distribution(
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/operations/prepare.py", line 49, in _get_prepared_distribution
    abstract_dist.prepare_distribution_metadata(finder, build_isolation)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/distributions/source/legacy.py", line 37, in prepare_distribution_metadata
    self._setup_isolation(finder)
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_internal/distributions/source/legacy.py", line 90, in _setup_isolation
    reqs = backend.get_requires_for_build_wheel()
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_vendor/pep517/wrappers.py", line 151, in get_requires_for_build_wheel
    return self._call_hook('get_requires_for_build_wheel', {
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_vendor/pep517/wrappers.py", line 255, in _call_hook
    raise BackendUnavailable(data.get('traceback', ''))
pip._vendor.pep517.wrappers.BackendUnavailable: Traceback (most recent call last):
  File "/tmp/t/.venv/lib/python3.8/site-packages/pip/_vendor/pep517/_in_process.py", line 63, in _build_backend
    obj = import_module(mod_path)
  File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 973, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'setuptools'

Using pip 19.3.1.

Let me know if this needs a news fragment, since I'm not even sure this is correct and if using pip to install setuptools is supported etc.

[benoit-pierre]

See discussion in #1644.

[blueyed]

@benoit-pierre thanks for the link, but I do not feel like wading through this. Leaving this as-is - it was just what I've done to make it work. Feel free to close etc.

[jaraco]

Based on my (quick) reading of #1644, I believe #1927 is the prescribed fix, but thanks anyhow to @blueyed for increasing the visibility (and urgency) of the issue.