Workaround for clang 3.2 libc++ empty struct bug.

Certain tests have empty structs or classes.
This encounters a bug with clang: http://llvm.org/bugs/show_bug.cgi?id=16764
This is fixed in later versions of clang, but not the version
currently bundled with Mavericks and XCode 5

Examples/test-suite/smart_pointer_inherit.i

@@ -47,6 +47,7 @@
 
 %inline %{
 class ItkLevelSetNodeUS2 {
+  int x;
 };
 %}