mainline AIX bootstrap broken in libstdc++-v3

[Benjamin Kosnik]

>P.S. Let's deal separately with the first issue...

So. 

> Are all allocators compiled even when not used?

Yes. We do this so that, when a different allocator is desired and
configured via --enable-libstdcxx-allocator, we don't have to play games
with any of the instantiation files.

There are ways around this, by adding complexity, that frankly are not
worth it.

-benjamin