Fix bugs in and expand syscall emulation code.
Fix bugs in and expand syscall emulation code.

arch/alpha/fake_syscall.cc:
    Fix a couple of bugs:
    - error return codes weren't making it through due to inadvertent cast to unsigned
    - sigreturn broken in not one but two ways
    - make all file descriptors look like plain files (not ttys)
    Added implementations of setuid, getgid, fcntl, and getdirentries from Dave Oehmke

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