RFA: RL78: Minor prologue and epilogue enhancements

Hi DJ, The patch below contains two minor enhancements for the RL78 prologue and epilogue code. The first is for when a large amount of local stack space needs to be allocated. Rather than generating a long sequence of SUB SP, #byte instructions, the patched codes moves SP into AX,

Re: RFA: RL78: Minor prologue and epilogue enhancements

OK to apply ? Ok.