AROS: massively enhanced i386 startup code, including
- fixed to always update the stacksize in __stklen, so the RTL knows the correct stacksize (StackLength in system unit is correct)
- this probably also fixes stack checking or opens the way to have a working stack checking on AROS, but that was not tested
+ call PASCALMAIN via exec/NewStackSwap() and provide a larger stack when the pre-set value is higher than what the system provides
+ use operatingsystem_result to simplify return code handling

These changes bring the AROS startup's stack handling to the Amiga/m68k and MorphOS level


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28611 3ad0048d-3df7-0310-abae-a5850022a9f2