m32r.h (RETURN_ADDR_RTX): Define.

* config/m32r/m32r.h (RETURN_ADDR_RTX): Define.
  (INCOMING_RETURN_ADDR_RTX): Define.
* config/m32r/m32r-protos.h (m32r_return_addr): Added.
* config/m32r/m32r.c (m32r_exppand_prologue): Changed for
  __builtin_return_address(0).
  (m32r_return_addr): Added for __builtin_return_address(0).
  (m32r_reload_lr): Ditto.

From-SVN: r83171