Cannot compile Slicer on Mac - macOS Sierra + clang 9 + cmake 3.9.1

[fedorov (Andrey Fedorov)]

I confirm - build succeeded.

[jcfr (Jean Christophe Fillion Robin (Kitware))]

SimpleITK build should be fixed by https://github.com/Slicer/Slicer/pull/802

@blowekamp Let me know what you think