port 037200e6 (r42486)

  original commit message:
  The IA32AddPair and IA32SubPair instructions were using an input register as a
  temporary value, which led to registers sometimes being clobbered when they
  shouldn't have been. This led to problems, for example, in calling printf to
  format doubles:

  printf("%f", 1.2345) => 0.61725 (on x86)

BUG=

Review-Url: https://codereview.chromium.org/2645233002
Cr-Commit-Position: refs/heads/master@{#42587}