port 1b230799 (r34747)

  original commit message:
  Int64Add is lowered to a new turbofan operator, Int32AddPair. The new
  operator takes 4 inputs an generates 2 outputs. The inputs are the low
  word of the left input, high word of the left input, the low word of the
  right input, and high word of the right input. The ouputs are the low
  and high word of the result of the addition.

BUG=

Review URL: https://codereview.chromium.org/1806833002

Cr-Commit-Position: refs/heads/master@{#34803}