Rearranged paravirt function vector.

- exit right below 6502 vectors.
- keep exit addr stable as it may be called from asm.

libsrc/sim6502/paravirt.s

@@ -7,11 +7,11 @@
 ; int __fastcall__ write (int fd, const void* buf, unsigned count);
 ;
 
-        .export         args, exit, _open, _close, _read, _write
+        .export         exit, args, _open, _close, _read, _write
 
-args            := $FFF0
-exit            := $FFF1
-_open           := $FFF2
-_close          := $FFF3
-_read           := $FFF4
-_write          := $FFF5
+_open           := $FFF4
+_close          := $FFF5
+_read           := $FFF6
+_write          := $FFF7
+args            := $FFF8
+exit            := $FFF9