Threads & exceptions

[Andrey Slepuhin]

Hi Teemu,
Returning to thread-safe exception handling, I finally checked
that having top_elt as static array cause invalid program
execution. So, I repost your changes solving this problem as
a patch against egcs-980122.

Regards,
Andrey.

P.S. I also attached a tiny patch for gthr.h to enable correct
     includes for AIX. Unfortunately I'm still confused how
     I should setup multilib correctly to disable cpu-specific
     library versions, but to enable thread-safe ones.