[PATCH] setup: use setuptools on Windows (issue5400)

[Gregory Szorc]

# HG changeset patch
# User Gregory Szorc <gregory.szorc at gmail.com>
# Date 1489118392 28800
#      Thu Mar 09 19:59:52 2017 -0800
# Node ID b51f9adb41e68d9f3d88582f044d2742ae29ce09
# Parent  cd29673cebdbe2d998009322e4c3657389d6aed0
setup: use setuptools on Windows (issue5400)

We've had a long, complicated history with setuptools. We want to
make it the universal default. But when we do, it breaks things.

`python setup.py build` is broken on Windows today. Forcing
the use of setuptools via FORCE_SETUPTOOLS=1 unbreaks things.

Since the previous bustage with making setuptools the default
was on !Windows, it seems safe to move ahead with the setuptools
transition on Windows. So this patch does that.

diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -63,7 +63,10 @@ import re
 import shutil
 import tempfile
 from distutils import log
-if 'FORCE_SETUPTOOLS' in os.environ:
+# We have issues with setuptools on some platforms and builders. Until
+# those are resolved, setuptools is opt-in except for platforms where
+# we don't have issues.
+if os.name == 'nt' or 'FORCE_SETUPTOOLS' in os.environ:
     from setuptools import setup
 else:
     from distutils.core import setup