This implements the five sign extension opcodes for ia32 and x64 (and
bails out on other architectures).

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Ibb8bae0e229e276b346f2d054b51864a0995a096
Reviewed-on: https://chromium-review.googlesource.com/1174533
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55898}