PATCH (libstdc++-v3 mainline): Re-enable i386/atomicity.h

[Benjamin Kosnik]

>Most interestingly, IMO, is the usage of these operations in
>basic_string. It would be interesting to find out how often atomic_add
>is used in an application that makes intense use of std::string.

This is also of interest to me. I think that Paolo has recently found
some MT string tests, so maybe this will be answered more definitively
in the future. Perhaps he can cc you on his results.

-benjamin