* internals.h: Declare __pthread_max_stacksize.
* pthread.c (__pthread_max_stacksize): New variable.
(__pthread_initialize_manager): Determine __pthread_initialize_manager
value.
* manager.c (thread_segment): Return always NULL if FLOATING_STACKS.
(pthread_allocate_stack): Allow kernel to choose stack address if
FLOATING_STACKS. This also handles variable-sized stacks.
Always allocate stack and guardoage together. Use mprotect to
change guardpage access.
* sysdeps/i386/useldt.h: Define FLOATING_STACKS and
ARCH_STACK_MAX_SIZE.
* attr.c (__pthread_attr_setstacksize): Also test value against
upper limit.
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