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.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2218023002
Cr-Commit-Position: refs/heads/master@{#38383}