Basically recognize certain x < y ? x : y constructs and turn that into
Float64Min/Float64Max operations, if the target machine supports that.
On x86 we lower to (v)minsd/(v)maxsd.

R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/998283002

Cr-Commit-Position: refs/heads/master@{#27160}