So far we treated SignedSmall and Signed32 feedback the same for number
operations. However it would be beneficial to generate (a lot) less code
if we only do a Smi check on the inputs instead of doing the full Smi +
HeapNumber + conversion check that we need to do for Signed32 feedback.

R=epertoso@chromium.org
BUG=v8:4583

Review-Url: https://codereview.chromium.org/2207893002
Cr-Commit-Position: refs/heads/master@{#38290}