PATCH [gcc and libstdc++] for memory barriers in staticinitalization

[David Edelsohn]

	The atomicity support for AIX is in the os/aix directory, not the
cpu/powerpc directory.

	AIX provides wrapper routines for atomic operations, but not for
sync.  I think atomic_word.h needs to be added to os/aix.  Unfortunately
it needs tests for the various versions of AIX and various architectures.
POWER did not support MP.  Only recent versions of the AIX assembler
understands lwsync, for instance.  GCC can assume recent versions of GAS,
but not OS toolchain.

	When you commit the patch, I will try to add a version for AIX.

David