Pull in r361696 from upstream llvm trunk (by Sanjay Patel):

Pull in r361696 from upstream llvm trunk (by Sanjay Patel):

  [SelectionDAG] soften assertion when legalizing narrow vector FP ops

  The test based on PR42010:
  https://bugs.llvm.org/show_bug.cgi?id=42010

  ...may show an inaccuracy for PPC's target defs, but we should not be
  so aggressive with an assert here. There's no telling what
  out-of-tree targets look like.

This fixes an assertion when building the graphics/mesa-dri port for
PowerPC64.

Reported by:	Mark Millard <marklmi26-fbsd@yahoo.com>
PR:		238082
MFC after:	3 days