objc fix for egcs-1.0.[23]

[Matthias Klose]

objc programs compiled with egcs-1.0.2 (i486-linux) seg faults. (see
"objc hello.m seg faults, by jdassen@wi.leidenuniv.nl, Thu, Apr 1998)
Using gcc/objc/thr-posix.c from the latest snapshot makes objc work.
It would be nice to see this fix in 1.0.3.

	Thanks, Matthias

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