Add another test for Ada Wide_Wide_String

In an earlier patch, I had written that I wanted to add this test:

      ptype Wide_Wide_String'("literal")

... but that it failed with the distro GNAT.  Further investigation
showed that it could be made to work by adding a function using
Wide_Wide_String to the program -- this caused the type to end up in
the debug info.

This patch adds the test.  I'm checking this in.