PATCH: GCC-3.0.4 (pre) on AIX requires pthreads

[David Edelsohn]

	Thanks for developing this patch.  This does install the correct
headers and does the right thing for AIX when the AIX configuration
reports its thread model as "aix" instead of using the THREAD_MODEL_SPEC
override.

	I hope that the libstdc++ maintainers will approve this patch so
that you can install it.  I will then remove the THREAD_MODEL_SPEC from
the AIX coniguration and AIX will no longer have a pthread dependency
introduced by the headers.

Thanks, David