libstdc++ compatibility

[Jason Merrill]

>>>>> Jeffrey A Law <law@cygnus.com> writes:

 > So, in the future if you could build these old libstdc++ releases with a 
 > new compiler and get something that is compatible for code which linked
 > against the old libstdc++ you'd be OK?

 > We certainly can't do it yet, but it might be something we can pull off in
 > the future.

Why can't they just ship the old binary built with the old compiler?

 > The question in my mind is how can we test this functionality?  Just being
 > able to build the old library isn't enough, we have to verify to some extent
 > that it is compatible with the old one.

 > We've also got to get a handle on when we actually make incompatible
 > changes.  We've started thinking about that some, but not enough IMHO.

Yes.  We should have tests for binary compatibility in the testsuite, so we
catch inadvertent breakages.

Jason