[Bug libstdc++/80276] pretty printer for std::unique_ptr shows type as std::unique_ptr

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80276

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We can prevent this by always casting the stored pointer to void*

        self.pointer = self.pointer.cast(gdb.lookup_type("void").pointer())