Changed all syscalls to use syscall return object.

Changed all syscalls to use syscall return object.

arch/alpha/alpha_linux_process.cc:
arch/alpha/alpha_tru64_process.cc:
cpu/exec_context.hh:
sim/process.hh:
sim/syscall_emul.cc:
sim/syscall_emul.hh:
    Changed all syscalls to use syscall return object
arch/alpha/isa_traits.hh:
    Added syscall return object that packages return value and return
    status into an object.
sim/process.cc:
    renamed variable name to nm so base class function name() can be called

--HG--
extra : convert_revision : 6609c5ffecc9e3519d7a0cd160879fd21d54abfc