#4068 uCsim issue with huc6280

[Gabriele Gorla]

uCsim has issues when using -t6280
many simulations fail with stack overflow.
attached files are from plain mos6502 build which should work unchanged on huc6280

uCsim commands:

set error stack on
set hw simif rom 0xfff0
step 500000000 vclk
state

gorlik@a64:/mnt/scratch/build/sdcc/sdcc-svnt/sdcc/support/regression$ ../../sim/ucsim/src/sims/mos6502.src/ucsim_mos6502 -t6502 gen/uc6502/tst_bug-2357.ihx 
uCsim 0.9.9, Copyright (C) 1997 Daniel Drotos.
uCsim comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
0> 1395 words read from gen/uc6502/tst_bug-2357.ihx
set error stack on
set hw simif rom 0xfff0
step 500000000 vclk
state0> 0> --- Running: bug-2357.c
Running testBug
--- Summary: 0/4/1: 0 failed of 4 tests in 1 cases.

Stop at 0x0004ec: (110) Program stopped itself
F 0x0004ec
Simulated 18936 ticks (1.894e-02 sec)
Host usage: 0.002859 sec, rate=6.623027
0> 

gorlik@a64:/mnt/scratch/build/sdcc/sdcc-svnt/sdcc/support/regression$ ../../sim/ucsim/src/sims/mos6502.src/ucsim_mos6502 -t6280 gen/uc6502/tst_bug-2357.ihx 
uCsim 0.9.9, Copyright (C) 1997 Daniel Drotos.
uCsim comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
0> 1395 words read from gen/uc6502/tst_bug-2357.ihx
set error stack on
set hw simif rom 0xfff0
step 500000000 vclk
state0> 0> Stack overflow, PC=0x0

Stop at 0x000320: (108) F 0x000320
Simulated 10 ticks (1.000e-05 sec)
Host usage: 0.000044 sec, rate=0.226719
0>