Subzero silently allows inserting a 32-bit integer into a vector with
16-bit elements. This generates a pinsrd instruction, which requires
SSE4.1, even when specifying to only support SSE2. This change emits
a pinsrw instruction instead, which is SSE2.

Bug swiftshader:20

Change-Id: I37bd0ebb6d9cfdd2cdef4788e89e9672386c685e
Reviewed-on: https://swiftshader-review.googlesource.com/8450Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>