COMP: Update ITK: include workaround for recent MacOSX/XCode Debug build error

This commit fixes error discussed here:

http://slicer-devel.65872.n3.nabble.com/can-t-build-Slicer-SimpleITK-link-error-tt4037626.html

It update the Sllicer/ITK fork integrating the following workaround:

commit Slicer/ITK@cb4946d
Author: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>
Date: Mon Nov 14 15:00:39 2016 -0500

BUG: Fix MacOSX build error occruing with newer version of XCode

// Waiting these two patches are integrated into upstream ITK, we use
// static_cast for both Release and Debug:
//
// * WIP: Add SafeDownCast to LightObject classes
//   http://review.source.kitware.com/#/c/21499/
//
// * ENH: Add tests to demonstrate OSX dynamic_cast failure
//   http://review.source.kitware.com/#/c/21755/
//
// Details reported here: https://issues.itk.org/jira/browse/ITK-3490
//

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25535 3bd1e089-480b-0410-8dfb-8563597acbee