1) Preserve the v850 system-call-number register when handling a signal;
   otherwise system calls will not be correctly restarted afterwards
2) Correctly handle illegal insn exceptions, which need a special
   instruction to return (not reti), and save PC/PSW to a different place
2) Remove some unnecessary register saving in the trap handler
3) Consolidate various places that use the register save/restore macros
4) Eliminate some unused compile-time configuration stuff
5) A bit of whitespace and other syntactic cleanup