Undocumented requirement: setuptools

[dabrahams]

It looks like this was resolved for me by installing Python's setuptools package:

Autofilling 1-5...success.
Autofilling 1-6...success.
Recording autofilled block MergeState('swift-xcode', tip1='upstream/master', tip2='swift-xcode', goal='rebase')[0:2,0:7].
Attempting automerge of 4-6...failure.
Attempting automerge of 2-1...failure.
Switched to branch 'imerge/swift-xcode'
<stdin>:282: SyntaxWarning: invalid escape sequence '\W'
<stdin>:286: SyntaxWarning: invalid escape sequence '\W'
Traceback (most recent call last):
  File "<stdin>", line 15, in <module>
ModuleNotFoundError: No module named 'distutils'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 17, in <module>
ModuleNotFoundError: No module named 'distutils'
Auto-merging Source/cmGeneratorTarget_IncludeDirectories.cxx