[www] 3.2 ABI Compatibility issues

[Benjamin Kosnik]

According to
http://gcc.gnu.org/install/configure.html

--enable-shared is on by default.

Due to Jakub's patching this week,

--enable-threads=posix

is now on by default.

Thus, it seems like the only really required flag in 3.2 will be:

--enable-__cxa_atexit

> E.g., it should be possible to learn the state of --enable-threads and
> --enable-__cxa_atexit .  That seems better than forcing users to guess
> how to build a new compiler with the most compatible C++ ABI.

I'm of the opinon that the default options for a platform should be
the ones used. 

This seems difficult to do with __cxa_atexit, thus your web page.

I think the verbose output in 'g++ -v' that indicates thread model
came about because nobody could figure out (easily) what was going on
when end-users reported bugs with MT apps. Having that info readily
available has made all of the FAQ-type questions much easier to deal
with.

I hope the same thing happens with ABI issues. Sure, you can scan
auto-host.h for DEFAULT_USE_CXA_ATEXIT, but it would seem simpler to
have ABI-breaking flags as easy for people figure out as possible.

-benjamin