port 40bdbef9 (r35131)

  original commit message:
  Int64Mul is lowered to a new turbofan operator, Int32MulPair. 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 multiplication.

BUG=

Review URL: https://codereview.chromium.org/1845183002

Cr-Commit-Position: refs/heads/master@{#35146}