Pull in r211435 from upstream llvm trunk (by Benjamin Kramer):

  Legalizer: Add support for splitting insert_subvectors.

  We handle this by spilling the whole thing to the stack and doing the
  insertion as a store.

  PR19492. This happens in real code because the vectorizer creates
  v2i128 when AVX is enabled.

This fixes a "fatal error: error in backend: Do not know how to split
the result of this operator!" message encountered during compilation of
the net-p2p/libtorrent-rasterbar port.

Reported by:	Evgeniy <iron@mail.ua>
MFC after:	3 days