Tweak exit() message.
Tweak exit() message.

sim/syscall_emul.cc:
    Make message for exit() more obvious.

hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,hoangt/tpzsimul.gem5,vovojh/gem5,vovojh/gem5