COMP: Workaround to fix HAVE_STAT redefined warning in SlicerDICOMExportDialog

This commit fixes the following warning:

//-----------
In file included from /path/to/Slicer-build/DCMTK/dcmdata/include/dcmtk/dcmdata/dcdatset.h:26:0,
from /path/to/Slicer-build/CTK/Libs/DICOM/Core/ctkDICOMItem.h:28,
from /path/to/Slicer-build/CTK/Libs/DICOM/Core/ctkDICOMDatabase.h:29,
from /path/to/Slicer/Modules/Scripted/DICOMLib/Widgets/qSlicerDICOMExportDialog.cxx:55:
/path/to/Slicer-build/DCMTK-build/config/include/dcmtk/config/osconfig.h:540:0: warning: "HAVE_STAT" redefined [enabled by default]
#define HAVE_STAT 1
^
In file included from /path/to/Slicer-build/python-install/include/python2.7/Python.h:58:0,
from /path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtPythonInclude.h:93,
from /path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQtInstanceWrapper.h:45,
from /path/to/Slicer-build/CTK-build/CMakeExternals/Install/include/PythonQt/PythonQt.h:46,
from /path/to/Slicer/Modules/Scripted/DICOMLib/Widgets/qSlicerDICOMExportDialog.cxx:46:
/path/to/Slicer-build/python-install/include/python2.7/pyport.h:361:0: note: this is the location of the previous definition
#define HAVE_STAT
^
//-----------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23955 3bd1e089-480b-0410-8dfb-8563597acbee