COMP: Handle compiler not supporting "pragma diagnostic".
COMP: Handle compiler not supporting "pragma diagnostic".

This commit fixes warnings introduced in InsightSoftwareConsortium/ITK@eb2316a
(BUG: TransformIO: Implement explicit template instantiation using "extern".)
by handling version of GCC not supporting "pragma diagnostic"
preprocessor instruction.

It does so by using the new ITK macros introduced in ITK
commit (COMP: TransformIO: Handle compiler not supporting "pragma
diagnostic".)

KitwareMedical/ITKIOTransformDCMTK,InsightSoftwareConsortium/ITKIOTransformDCMTK,InsightSoftwareConsortium/ITKIOTransformDCMTK,KitwareMedical/ITKIOTransformDCMTK,InsightSoftwareConsortium/ITKIOTransformDCMTK