It turns that despite the fact Slicer build system already download setuptools, SimpleITK is also attempting to download its own.

This is explained because Slicer version is 1.4.2 and SimpleITK expects at least version 2.2. See [2]

By updating Slicer build system to download the most recent version of setup tools, it should avoid each project to download their own.

[1] https://github.com/Slicer/Slicer/blob/020a08d9a23318578f5fe5e0d5c39d0fe43b82c1/SuperBuild/External_python-setuptools.cmake#L21

[2] https://github.com/SimpleITK/SimpleITK/blob/3fe73688f9b670b590a0cd4d3ecc3c4a2a0f8029/Wrapping/PythonPackage/ez_setup.py#L33

Fixed in r23421
See http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=23421

// -------------------
OMP: Prevent windows build freeze when downloading setuptools 2.2

Updates setuptools from version 1.4.2 to 5.3

This commit fixes 0003763 by ensuring a recent version of setuptools
is used by all projects. Having a recent version of setuptools in the
python path will prevent SimpleITK (and other project) from trying
to download older setuptools will avoid the possible freeze.

This commit also patches the "setup.py" provided by pydicom to avoid
downloading an old version of distribute. This is done by removing the
first 3 lines of setup.py that were using an ancient distribute_setup.py.

Finally, after some testing recent version of setuptools (5.3 in the present
case) does NOT prevent incorrect update of "easy-install.pth" in case of
concurrent installs.
The issue distribute issue 389 [1] also mentioned in Slicer issue 0003757 [2]
is still current.

[1] https://bitbucket.org/tarek/distribute/issue/389/concurrent-installations-can-lose-updates
[2] http://www.na-mic.org/Bug/view.php?id=3757
// -------------------