-Werror=deprecated-copy (GCC trunk towards GCC 9)

Change-Id: I12d5cfafab17e02dc041eff8af207ba36df9bb5a
Reviewed-on: https://gerrit.libreoffice.org/56938
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

slideshow/source/inc/shapesubset.hxx

@@ -91,6 +91,12 @@ namespace slideshow
 
             ~ShapeSubset();
 
+            // For a rationale for this hacky combination of user-provided dtor, defaulted copy
+            // ctor, and deleted copy assignment op, see the "TODO(Q1)" comment in
+            // CloningNodeCreator (slideshow/source/engine/animationnodes/animationnodefactory.cxx):
+            ShapeSubset(ShapeSubset const &) = default;
+            void operator =(ShapeSubset) = delete;
+
             /** Get the actual subset shape.
 
                 If the subset is currently revoked, this method