port f68059b7 (r38383)

  original commit message:
  Benedikt, do you think we could also provide these operators on mips,
  maybe by expanding them to "-0.0 -x"? If mips can provide these operators,
  then we could make Float64Neg and Float32Neg real operators and not just
  OptionalOperators.

BUG=

Review-Url: https://codereview.chromium.org/2223793002
Cr-Commit-Position: refs/heads/master@{#38464}