no more common syscall emulation, now common for everyone

no more common syscall emulation, now common for everyone
check abi-tag note section of elf binary for OS
add pseudo functions (moved from alpha and made to be generic)
move setsyscallreturn into isa traits

arch/alpha/SConscript:
    no more common syscall emulation, now common for everyone
arch/alpha/isa_traits.hh:
    move setsyscallreturn into isa description
arch/alpha/linux/process.cc:
arch/alpha/tru64/process.cc:
    use generic functions rather than alpha specific ones
arch/sparc/isa_traits.hh:
    have consts for generic pseudo syscalls
arch/sparc/linux/process.cc:
    use generic functions
base/loader/elf_object.cc:
    check abi-tag note section of elf binary for OS
cpu/exec_context.hh:
    move syssyscallreturn into isa traits
sim/process.cc:
    find call num with a more generic
sim/syscall_emul.cc:
sim/syscall_emul.hh:
    add pseudo functions (moved from alpha and made to be generic)

--HG--
extra : convert_revision : 5a31024ecde7e39b830365ddd84593ea501a34d2