RFR(S): 8186293: [aix] Fix thread creation with huge stack sizes

[Lindenmaier, Goetz]

Hi,

TestOptionWithRanges causes the vm on aix to crash on some machines.
This is because huge stack sizes are not treated properly.

On linux, pthread_attr_setstacksize succeeds if called with huge values, but
pthread_create() then fails. On Aix, pthread_attr_setstacksize  fails if
passed a value exceeding the limits and leaves the minimal system
thread stack size in attr. Thus thread creation succeeds and leads to
crashes after thread creation when the guard pages shall be protected
but don't fit on the tiny stack created.

Please review this small, aix-only change.
http://cr.openjdk.java.net/~goetz/wr17/8186293-aixHugeStack/webrev.01/

Best regards,
  Goetz.