MFC r256090:

Pull in r192064 from upstream llvm trunk:

  X86: Don't fold spills into SSE operations if the stack is unaligned.

  Regalloc can emit unaligned spills nowadays, but we can't fold the
  spills into SSE ops if we can't guarantee alignment. PR12250.

This fixes unaligned SSE accesses (leading to a SIGBUS) which could
occur in the ffmpeg ports.

Reported by:	tijl