Add x86 vector packing instructions.

BUG=swiftshader:15

Change-Id: I0d40fab6287130143693e8e4752859b7142a503d
Reviewed-on: https://chromium-review.googlesource.com/394007
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Jim Stichnoth <stichnot@chromium.org>
15 files changed