BUG: backport ITKv4 fix for clang build

See:
* http://review.source.kitware.com/#change,3447
* http://llvm.org/bugs/show_bug.cgi?id=9395

Utilities/ITK/Code/Common/itkImageSource.h

@@ -229,7 +229,7 @@ protected:
    * \sa GenerateData(), SplitRequestedRegion() */
   virtual
   void ThreadedGenerateData(const OutputImageRegionType& outputRegionForThread,
-                            int threadId ) ITK_NO_RETURN;
+                            int threadId );
 
 
   /** The GenerateData method normally allocates the buffers for all of the

Utilities/ITK/Code/Common/itkMacro.h

@@ -960,23 +960,6 @@ private:
 # define ITK_TEMPLATE_EXPLICIT 0
 #endif
 
-
-//----------------------------------------------------------------------------
-// Macro to declare that a function does not return. __attribute__((noreturn))
-//    On some compiler, functions that do not return (ex: exit(0)) must
-//    have the noreturn attribute. Otherwise, a warning is raised. Use
-//    that macro to avoid those warnings. GCC defines the attribute
-//    noreturn for versions 2.5 and higher.
-#if defined(__GNUC__)
-#  if (((__GNUC__ == 2) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ >= 3))
-#    define ITK_NO_RETURN \
-       __attribute__ ((noreturn))
-#  endif
-#else
-#  define ITK_NO_RETURN
-#endif
-
-
 #ifdef ITK_USE_TEMPLATE_META_PROGRAMMING_LOOP_UNROLLING
 //--------------------------------------------------------------------------------
 //  Helper macros for Template Meta-Programming techniques of for-loops unrolling