BUG: #3040 build DCMTK as shared libraries

This avoids issues where dcmtk code is statically linked into more
than one shared library, meaning that some static initialization
and destructor code is being invoked more than once.  See the bug
report for details.

http://www.na-mic.org/Bug/view.php?id=3040

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21914 3bd1e089-480b-0410-8dfb-8563597acbee