Error when building Windows wheels locally on Python 3.8

Hi, there seems to be a bug in the wheel building process that manifests itself on Python 3.8.2, and I'm not sure what the cause is. The error (`ERROR_SHARING_VIOLATION`) is as follows. I've redacted/replaced the directory names with environment variables etc.:

(**Temporary workaround**: Pass `--no-clean` to pip to avoid cleaning the build directory.)

$ DISTUTILS_DEBUG=1 pip install --no-cache-dir --force-reinstall --no-deps dm-tree
Collecting dm-tree
Downloading https://files.pythonhosted.org/packages/70/0a/bc3e9865603332c525fc218aceb023762aeffc2a86ff99b347b67ee3f2a8/dm-tree-0.1.5.tar.gz
Installing collected packages: dm-tree
Running setup.py install for dm-tree ... done

Exception:
Traceback (most recent call last):
File "miniconda3\lib\shutil.py", line 617, in _rmtree_unsafe
os.rmdir(path)
PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: '%TEMP%\\2\\pip-install-j0filgug\\dm-tree'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "miniconda3\lib\site-packages\pip\_internal\basecommand.py", line 228, in main
status = self.run(options, args)
File "miniconda3\lib\site-packages\pip\_internal\commands\install.py", line 380, in run
return ERROR
File "miniconda3\lib\site-packages\pip\_internal\utils\temp_dir.py", line 58, in __exit__
self.cleanup()
File "miniconda3\lib\site-packages\pip\_internal\utils\temp_dir.py", line 81, in cleanup
rmtree(self.path)
File "miniconda3\lib\site-packages\pip\_vendor\retrying.py", line 49, in wrapped_f
return Retrying(*dargs, **dkw).call(f, *args, **kw)
File "miniconda3\lib\site-packages\pip\_vendor\retrying.py", line 212, in call
raise attempt.get()
File "miniconda3\lib\site-packages\pip\_vendor\retrying.py", line 247, in get
six.reraise(self.value[0], self.value[1], self.value[2])
File "miniconda3\lib\site-packages\pip\_vendor\six.py", line 693, in reraise
raise value
File "miniconda3\lib\site-packages\pip\_vendor\retrying.py", line 200, in call
attempt = Attempt(fn(*args, **kwargs), attempt_number, False)
File "miniconda3\lib\site-packages\pip\_internal\utils\misc.py", line 107, in rmtree
shutil.rmtree(dir, ignore_errors=ignore_errors,
File "miniconda3\lib\shutil.py", line 737, in rmtree
return _rmtree_unsafe(path, onerror)
File "miniconda3\lib\shutil.py", line 610, in _rmtree_unsafe
_rmtree_unsafe(fullname, onerror)
File "miniconda3\lib\shutil.py", line 619, in _rmtree_unsafe
onerror(os.rmdir, path, sys.exc_info())
File "miniconda3\lib\site-packages\pip\_internal\utils\misc.py", line 120, in rmtree_errorhandler
func(path)
PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: '%TEMP%\\2\\pip-install-j0filgug\\dm-tree'