patch for presumed typo in boehm-gc/misc.c

[Per Bothner]

Well, my fix doesn't work.  GC_clear_stack_inner is *also* not being
defined.  This is on Red Hat 7.0, on a i686.  I guess the first
question is:  *should* GC_clear_stack_inner be defined?

I configured with --enable-threads.  I see in misc.c the following:

#if defined(ASM_CLEAR_CODE) && !defined(THREADS)
  extern ptr_t GC_clear_stack_inner();
#endif  

#if !defined(ASM_CLEAR_CODE) && !defined(THREADS)
/* Clear the stack up to about limit.  Return arg. */
/*ARGSUSED*/
ptr_t GC_clear_stack_inner(arg, limit)
ptr_t arg;
word limit;
{
  ...
}
#endif

So GC_clear_stack_inner is only defined if THREADS is defined.  But
GC_clear_stack calls GC_clear_stack_inner whether or not THREADS is
defined (using two different pieces of code).
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/