The fallback for {Pinsrd} and {Pextrd} for the non-avx and non-sse
variant clobbered the {xmm0} register. This CL fixes this by storing
the values on the stack and modifying them there instead.
The alternative would have been to pass in a scratch register. But this
path is not commonly used and we cannot express in the API whether the
scratch register is needed or not. So we would sometimes have to spill a
register to pass it as scratch register even though it is then unused.

R=titzer@chromium.org
CC=​mstarzinger@chromium.org

Bug: v8:6600
Change-Id: Ieae53b892cc55eed4fcfa3d0e7f82f3e1afe72be
Reviewed-on: https://chromium-review.googlesource.com/1219633Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55800}