[Bug c++/65047] [c++17] Add support for nested namespace defintions.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65047

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Patches should go to the gcc-patches list not bugzilla (it's not a bug that we
have incomplete support for an incomplete draft standard)