Add support for scalarizing/splitting vector bswap.

Summary:
  SLP Vectorization of intrinsics (r203707) has exposed cases where the
  expansion of vector bswap is failing (PR19151).

Reviewers: hfinkel

CC: chandlerc

Differential Revision: http://llvm-reviews.chandlerc.com/D3104

llvm-svn: 204163
2 files changed