* blockframe.c (frameless_look_for_prologue): Speed up by

    * blockframe.c (frameless_look_for_prologue):  Speed up by
        calling SKIP_PROLOGUE_FRAMELESS_P if it's defined.
        * tm-sparc.h (SKIP_PROLOGUE, SKIP_PROLOGUE_FRAMELESS_P):
        Define two variants, one faster.
        * sparc-tdep.c (sparc_frame_chain):  Use target_read_memory
        and return zero, rather than giving an error.
        (setup_arbitrary_frame):  Initialize the PC in the new frame.
        (skip_prologue):  Add a second arg saying whether we're just
        checking for a frameless function or not.