Add support for vector types.

- Add vector types to the type table.

- Add support for parsing vector types in llvm2ice.

- Legalize undef vector values to zero. Test that undef vector values are lowered correctly.

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

Review URL: https://codereview.chromium.org/353553004
12 files changed