libstdc++-v3 won't build on AIX 4.1 any more (3.0 branch)

[Benjamin Kosnik]

> Indeed, config/os/generic/bits/atomicity.h doesn't exist.
                 ^^

this should be cpu

> I suppose the case that matches aix* to define ATOMICITYH should be
> made stricter so as to match only AIX 4.3 or newer, like the case that
> sorts os_include_dir does?

yeah I thought I did this already but perhaps not