port 40bdbef9

 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.

R=titzer@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1849543003

Cr-Commit-Position: refs/heads/master@{#35167}