This implements the full set of f32 comparisons (f32.eq, f32.ne,
f32.lt, f32.gt, f32.le, f32.ge) on ia32 and x64.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: I2be786431d01b4ed540b70f3e4a27c19b7d2649e
Reviewed-on: https://chromium-review.googlesource.com/928982Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51545}