[Bug libstdc++/70081] New: 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

            Bug ID: 70081
           Summary: Document how to add new symbols to libstdc++ exports
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Keywords: documentation
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

Where to add symbols in linker script. How/when to use a new symbol version.
How to bump the libtool version. How to update the testsuite to know about new
symbol versions. How to update baselines (this might already be documented).