For a * b with only truncated word32 uses (or result known to be in
signed32 range), we can use Int32Mul if we know for sure that the
intermediate result is inside the safe integer range, and a and b are
in signed32 range.

Drive-by-fix: Also use TypeCache in SimplifiedLowering.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1478953002

Cr-Commit-Position: refs/heads/master@{#32330}