[Bug libstdc++/77342] Use abi_tag on Debug Mode namespace

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77342

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-10-03
     Ever confirmed|0                           |1