On MacOSX factory, update compiler version to cland-3.1

This help fixing the error discussed in [1]

[1] http://slicer-devel.65872.n3.nabble.com/MacOSX-factory-build-Transitioning-from-hybrid-quot-llvm-g-quot-to-quot-clang-quot-Update-to-Qt-4-8-6-td4032198.html