[Bug c++/29556] Expect error when 'using namespace std' is declared when std namespace is not defined

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=29556

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
      Known to fail|                            |
   Last reconfirmed|2006-10-23 00:48:57         |2021-7-23

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
We should at least warn this is an extension like clang does:
<source>:1:17: warning: using directive refers to implicitly-defined namespace
'std'