Pull in r182656 from upstream llvm trunk:

  LoopVectorize: LoopSimplify can't canonicalize loops with an
  indirectbr in it, don't assert on those cases.

  Fixes PR16139.

This should fix clang assertion failures when optimizing at -O3, similar
to:

  Assertion failed: (TheLoop->getLoopPreheader() && "No preheader!!"),
  function canVectorize, file
  contrib/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp, line 2171.

Reported by:	O. Hartmann <ohartman@zedat.fu-berlin.de>
PR:		ports/178332, ports/178977
MFC after:	3 days