Add support for passing and returning vectors in accordance with the x86 calling convention.

- Add TargetLowering::lowerArguments() as a new stage in TargetLowering.
- Add support for passing arguments/return values in XMM registers in the x86 target.

BUG=none
R=jvoung@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/372113005
10 files changed