[Bug c++/103553] Show what decltype deduced in static_assert

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103553

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Yes, I added that in GCC 11.

To make this work, I think we'll have to print parser->scope when there's one. 
In this case it's

full-name "struct is_same<int&&, int>"

so that could be extracted and used in finish_static_assert.