[g++] find build_headers, toplevel

[Mark Kettenis]

   From: Alexandre Oliva <aoliva@redhat.com>
   Date: 18 Dec 2000 06:24:51 -0200

   IIRC, cxx_interface was supposed to be used as something that would
   change whenever the C++ ABI changed, even if the libstdc++ API
   remained constant.

   It would probably be a good idea to use libc_interface and
   cxx_interface when building libstdc++-v3's.  Libtool's -release flag
   would be the most appropriate to encode this information in the
   library SONAMEs.

The libc_interface stuff is nothing but a stop-gap for binary
compatibility problems caused by the tight coupling of glibc's libio
and the C++ part of libio that lives in the old libstdc++.  It
needlessly breaks binary compatibility in the glibc 2.1 to 2.2
transition (since it's based on the glibc release number, not on
changes in the ABI), and I doubt that there are any people that
*really* know why it was necessary for the glibc 2.0 to 2.1
transition.  I guess it was deemed acceptable since binary
compatibility for C++ was next to non-existant anyway.

*Please* don't use the same mechanism for libstdc++-v3.  For one
thing, the new C++ ABI breaks the libio coupling anyway, so there is
the opportunity to think of a better strategy.

Mark