This prepares fixes in the implementations of vabs and vneg (potentially
more). In order to implement them correctly, we need to preserve the
exact bit pattern.

R=ahaas@chromium.org, rodolph.perfetta@arm.com

Bug: v8:6947
Change-Id: I7194a60371a6e3c9ffba32981c90090ffafaa610
Reviewed-on: https://chromium-review.googlesource.com/722941Reviewed-by: Rodolph Perfetta <rodolph.perfetta@arm.com>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48648}