[CVS ci] exit opcode

[Leopold Toetsch]

I have checked in a small change:
- B<exit>(in INT) throws an exception with severity C<EXCEPT_exit> and 
the given exit status.
- the system itself doesn't through such an exception on runloop exit 
yet, this would need classifying exception handlers, so that not 
arbitrary user handlers would catch this exception, and some rework to 
print profiling/debug code.

I'd like to change the startup parameters too: move the ARGV array from 
P0 to P5. This would allow main to be:

.pcc_sub _main prototyped
   .param SArray ARGV
   .local int ARGC
   ARGC = ARGV
     ...
leo