Add UNIV_LIKELY and UNIV_UNLIKELY hints.
  cmp_dtuple_rec_with_match(): Move condition outside loop.
  Reduce the number of comparisons per iteration.
mtr0mtr.c:
  mtr_memo_slot_release(): Add a UNIV_LIKELY hint.
  Simplify the preprocessor magic.
buf0buf.c:
  buf_page_optimistic_get_func(): Add UNIV_UNLIKELY hints.
  Introduce an exit_func label to remove duplicated error exits.