[Bug tree-optimization/65443] Don't peel last iteration from loop in transform_to_exit_first_loop

["vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65443

--- Comment #6 from vries at gcc dot gnu.org ---
After looking into it a bit further, I think what we're trying to get is:
...
  <bb x>:
  goto <bb y>;

  <bb 4>:
  i_17 = (int) ivtmp_y;
  _7 = (long unsigned int) i_17;
  _8 = _7 * 4;
  _9 = pretmp_24 + _8;
  _10 = *_9;
  sum_11 = _10 + sum_y;
  i_12 = i_17 + 1;
  i.1_3 = (unsigned int) i_12;
  goto  <bb 6>;

  <bb 6>:
  ivtmp_6 = ivtmp_y + 1;
  goto <bb y>;

  <bb y>:
  # sum_y = PHI <1(x), sum_11(6)>
  # ivtmp_y = PHI <0(x), ivtmp_6(6)>
  if (ivtmp_y < _20 + 1)
    goto <bb 4>;
  else
    goto <bb 5>;

  <bb 5>:
  # sum_21 = PHI <sum_y(y), sum_26(8)>
  goto <bb 7>;
...