Switching the default for -fabi-version

[Mark Mitchell]

> Well, maybe someone with in depth knowledge of what ABI things
> have changed should chime in at this point and indicate what
> has actually changed :-)

The short answer is "in some classes, some fields will be at different
offsets".  But that sounds much more severe than it really is; the
longer answer is "in a few corner-case classes -- such as those with
lots of empty base classes, or those that have base classes that end
with bitfields -- the offsets of some virtual bases and/or fields might
change."

There are also a few places (involving complex templates) where the
mangled name of a function changed.
 
The descriptions of *what* changed aren't as important as the question
of *how much code* is affected.  And, when you bear in mind that the C++
runtime library is bumping its version number again, the answer is
"almost none".

-- 
Mark Mitchell <mark@codesourcery.com>
CodeSourcery, LLC