* Add initial support for code generation with SSE4.1 instructions. The
following operations are affected:
- multiplication with v4i32
- select
- insertelement
- extractelement
* Add appropriate lit checks for SSE4.1 instructions. Run the crosstests
in both SSE2 and SSE4.1 mode.
* Introduce the -mattr flag to llvm2ice to control which instruction set
gets used.
BUG=none
R=jvoung@chromium.org, stichnot@chromium.org
Review URL: https://codereview.chromium.org/427843002
