Added support for building big endian ARC elf toolchain.

2013-02-25  Simon Cook  <simon.cook@embecosm.com>

        * config.sub: Make arceb-* valid.
        * configure.ac: Make arceb-*-* valid.
        * configure: Regenerate.
bfd/
        * bfd/config.bfd: Make arc*-*-elf* valid for big endian ARC.
ld/
        * configure.tgt: Make arc*-*-elf* valid for big endian ARC.