[Bug libstdc++/70081] Document how to add new symbols to libstdc++ exports

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70081

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |7.0

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed at r239572