documenting C++ and libstdc++ ABI issues

[Joe Buck]

> On Tue, 27 Aug 2002, Janis Johnson wrote:
> 
> > This information is of interest to GCC users, not just developers, so
> > it should be in the GCC manual rather than the internals manual.
> 
> There's a need for user information about when ABI incompatibilities
> affect linking code built with different compilers or compiler versions.  
> But there's also a need for the technical documentation defining what the
> ABI is, where this goes beyond the external standards (e.g., the ABI for
> code using GCC extensions), and what the actual "3.2 ABI" is in cases
> where it differs from the specification (whereas the user documentation
> need only discuss what code is affected, not the detailed differences in
> those cases).  I feel that technical documentation fits better in the
> internals manual.

Users will wish to know how to avoid code that tweaks one of the
incompatibilities, and such an explanation could appear in the user
manual.  Beyond that, I'd agree that the main guts go in internals.