ENH: Update build system to more robustly check bitness using void ptr size

This commit update the build system so that void pointer size is used
instead of system process name.

[CTK]

$ git shortlog 9e8f66f..f34158 --no-merges
Jean-Christophe Fillion-Robin (1):
      Check bitness using void ptr size instead of system processor name

[DMCTK]

$ git shortlog f461865..042de27 --no-merges
Jean-Christophe Fillion-Robin (1):
      Update CMake build system to more robustly check bitness using void pointer size

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23805 3bd1e089-480b-0410-8dfb-8563597acbee
COMP: Update python - Fix configuration error on 32-bit system of type i686

The commit fixes the following error:

// ---------------
CMAKE_SYSTEM_PROCESSOR:i686

/home/thiele/Slicer-SuperBuild-Debug/python-build/../Python-2.7.3/Modules/_ctypes/libffi/src/i686/ffi.c

  Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
  .hxx .in .txx
Call Stack (most recent call first):
  cmake/extensions/CMakeLists.txt:183 (add_python_extension)

// ---------------

[python]

$ git shortlog 47845c5..ee53f79 --no-merges
Jean-Christophe Fillion-Robin (1):
      Fix configuration of ctypes extension in case system processor is i686



Thanks to  "Thiele Kobus <TKOBUS@partners.org>" for his help identifying
the issue.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23806 3bd1e089-480b-0410-8dfb-8563597acbee