Overlay (-fpic) support:

        * config/epiphany/epiphany.h (ASM_OUTPUT_SYMBOL_REF): Define.
        #if 0 for now because assembler is not ready.

        * config/epiphany/epiphany.h (EPIPHANY_LIBRARY_EXTRA_SPEC): Add -fpic.
        * config/epiphany/epiphany.md (GPR_FP): Change to 15.
        * config/epiphany/epiphany.c (TARGET_CAN_ELIMINATE): Define.
        (struct epiphany_frame_info) <initialized>: Now bool.
        (struct epiphany_frame_info) <frame_offset_known, sft_hd_frame_offset>:
        New members.
        (set_lr_slot_offset): New static function.
        (MUST_SAVE_REGISTER): If frame_pointer_needed, Save GPR_FP.
        (MUST_SAVE_RETURN_ADDR): Delete usused macro.
        (epiphany_compute_frame_size): Compute new current_frame_info
        members.  Avoid un-pairing double word register save.
        Pad pretend args if that helps building a post-decrement.
        Remove small_slots overhang.
        Allow GPR_LR and GPR_FP to be paired up.
        Make sure first_offset allows fits into add range.
        (epiphany_emit_save_restore): Use set_lr_slot_offset.
        (epiphany_expand_prologue): Remove unsued variable save_config.
        Record LR slot offset when encounterd at first_slot.
        Use add to set hard frame pointer where necessary.
        (epiphany_initial_elimination_offset): Use
        current_frame_info.sft_hd_frame_offset.
        (epiphany_can_eliminate): New static function.