Log Message:
   declare MACHINE_CPU.  MACHINE_CPU will be generated from MACHINE_ARCH,
   to identifiy CPU type in build tree (like mipse[lb] -> mips, sh3e[lb] -> sh3).
   
   XXX what should we do about arm and sparc?


what do you mean?  arm?? -> arm?  sparc leave alone?  the only time i'm
aware of where sparc & sparc64 are equivalent is in the guts of the
toolchain (gas/ld/bfd) which we don't really need to worry about.