Curent 3.0 branch of gcc fails to configure on AIX

[David Edelsohn]

>>>>> Alexandre Oliva writes:

Alexandre> How's this?  Ok to install?  Mainline and 3.0 branch?

Alexandre> * tm.texi (THREAD_MODEL_SPEC): Document it.
Alexandre> * gcc.c (main): Use it.
Alexandre> * config/rs6000/aix43.h (THREAD_MODEL_SPEC): Define it.

	Having GCC encapsulate the complexity and removing the cruft from
libstdc++-v3 definitely seems like a fine solution.  I'm sure Ben will be
happy (:^).

	Please go ahead and install it (it has been tested, I assume).
And please define THREAD_MODE_SPEC in aix51.h as well duplicating aix43.h.

Thanks, David