This enables emulating 64-bit and 32-bit vectors using 128-bit
vectors internally (x86 only for now). Note that these Intrinsics
are not part of the PNaCL specification.

BUG=swiftshader:15

Change-Id: I61a666243832c2856e60eb477d42a72dec07d01d
Reviewed-on: https://chromium-review.googlesource.com/392246Reviewed-by: Jim Stichnoth <stichnot@chromium.org>
Tested-by: Nicolas Capens <nicolascapens@google.com>