irix bootstrap failure in libstdc++ testsuite

[Billinghurst, David (CALCRTS)]

> You should have a file src/atomicity.o that has these definitions.
> 
> -benjamin

Thanks.

I see src/atomicity.o which has _ZN9__gnu_cxx18__exchange_and_addEPVli.
This demangles as __gnu_cxx::__atomic_add(long volatile*, int), so
that seems OK.  Will investigate.