Give a different name to the crosstest .s and .o files depending on the
CPU features as well. That way the SSE2 and SSE4.1 .s and .o are separate.

The encodings for Pextrw and Pextrb/d... make me sad.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/656983002