Programmatically disable coverage when running on PyPy.

Warn the user when distutils is present

Warn the user when distutils is present to discourage this usage and direct users to the recommended usage. Closes #2230.

Test Python 3.9-dev on GitHub Actions

Fix race in spawn

Allow spawn to accept environment. Avoid monkey-patching global state.

Allow spawn to accept environment. Avoid monkey-patching global state. Closes pypa/setuptools#2212 and closes pypa/distutils#5.

Change exec_module to load_module

Test Python 3.9-dev on Travis CI

Fixes #2246

Re-enable distutils adoption with escape hatch

Allow opt-in and opt-out of distutils adoption at run time with SETUPTOOLS_USE_DISTUTILS environment variable.

Remove py2warn

Refresh distutils

Merge commit 'bbe8e80b' of https://github.com/pypa/distutils into refresh-distutils

Automerge-Triggered-By: @jaraco

Remove py2_warn, no longer needed as a SyntaxError is encountered before the warning can be issueed.

Restore support for spawn when compiler is missing

Replace OSError with DistutilsExecError. Fixes pypa/distutils#3 and pypa/setuptools#2228 and bpo-41207.