Restructuring of LiveProcess etc. to support multiple emulated OS syscall

Restructuring of LiveProcess etc. to support multiple emulated OS syscall
interfaces, and specific support for Alpha Linux.  Split syscall emulation
functions into several groups, based on whether they depend on the specific
OS and/or architecture (and all combinations of above), including the use of
template functions to support syscalls with slightly different constants
or interface structs.

arch/alpha/alpha_tru64_process.cc:
    Incorporate full Tru64 object definition here, including structure and constant definitions.
    This way we can wrap all of the functions inside the object, and not worry about namespace
    conflicts because no one outside this file will ever see it.
base/loader/aout_object.cc:
base/loader/aout_object.hh:
base/loader/ecoff_object.cc:
base/loader/ecoff_object.hh:
base/loader/elf_object.cc:
base/loader/elf_object.hh:
base/loader/object_file.cc:
base/loader/object_file.hh:
    Add enums to ObjectFile to indicate the object's architecture and operating system.
cpu/exec_context.cc:
    prog.hh is now process.hh
cpu/exec_context.hh:
    prog.hh is now process.hh
    move architecture-specific syscall arg accessors into ExecContext
cpu/simple_cpu/simple_cpu.cc:
    No need to include prog.hh (which has been renamed)
sim/process.cc:
sim/process.hh:
    LiveProcess is now effectively an abstract base class.
    New LiveProcess::create() function takes an object file and dynamically picks the
    appropriate subclass of LiveProcess to handle the syscall interface that file expects
    (currently Tru64 or Linux).

--HG--
rename : arch/alpha/fake_syscall.cc => arch/alpha/alpha_tru64_process.cc
rename : sim/prog.cc => sim/process.cc
rename : sim/prog.hh => sim/process.hh
extra : convert_revision : 4a03ca7d94a34177cb672931f8aae83a6bad179a