Target specific ABI tweaks

[Phil Edwards]

> >What would be the preferred way to make these changes? I can't see any 
> >existing mechanisms for describing target differences from the generic C++ 
> >abi.
> 
> I believe Phil Edwards, anticipating this day, already did the work for
> target-specific linkage maps. You might want to ask him for suggestions.

For the record:

In configure.host, set port_specific_symbol_files accordingly.  Use whatever
linker script syntax is appropriate for the symver_map language in use.
Currently we have an extensive list of supported linkers:

  - gnu ld

Umm, yeah.  If users of other linkers want to version symbols, they'll
have to step up and write the symver map.


Phil

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