Switching the default for -fabi-version

[law@redhat.com]

In message <1066811338.4002.6.camel@minax.codesourcery.com>, Mark Mitchell writ
es:
 >
 >> which are not very clear (may vs. will) and omitting of a reason (in case
 >> of the second warning). So to say, if I can still specify -fabi-version=0
 >> I'm happy with changing. But you could try to make sure you dont break
 >> libstdc++ compatibility with this change?
 >
 >This is the point everyone seems to be missing: libstdc++ compatibility
 >is *already* going to break in GCC 3.4.
But as you know, not everyone uses libstdc++ ;-)  

 >And, what, really is the benefit of keeping the default compiler ABI
 >consistent with a previous version if the runtime library is going to
 >bump its major version number?
The ability to build plug-ins for popular packages such as Mozilla.

The ability to interoperate with existing C++ runtimes that may not be
libstdc++.

 >The only situation where the change I'm proposing would matter is when
 >you're using the new compiler with the old library.  That probably won't
 >work anyhow -- since, for example, the new parser probably can't handle
 >the old headers.
I wasn't aware of this.

 >But, if, somehow, it would work without the change, it will also work
 >with the change -- provided you add -fabi-version=1 to your command
 >line.
That may ultimately be the answer.  Bump up and allow folks who need it
to explicitly ask for the old ABI.  

jeff