There was an issue with passing float32 parameters, if the value was
spilled on the stack and passed as stack parameter.
First, we sometimes reduced the stack pointer by 8 bytes instead of 4,
and second, there was a mismatch between movsd and movss.

R=titzer@chromium.org

Bug: chromium:718858
Change-Id: Ia884df369ddd95adeff3733f9715f589996f0b65
Also-By: ahaas@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/684738Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48181}