AIX atomicity.h support

[David Edelsohn]

	So far I have the v3/math directory compiled after manually
working around math/complex-stub.h:cabs() prototype conflicting with AIX's
/usr/include/math.h:cabs().  I am not sure how to handle this conflict
automatically. 

	I currently am running into problems with libio/_G_config.h
because some types it is expecting are not being defined.  This could be a
result of the configuration process getting confused.

David