Merging r283129:

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r283129 | hans | 2016-10-03 11:18:04 -0700 (Mon, 03 Oct 2016) | 6 lines

Jump threading: avoid trying to split edge into landingpad block (PR27840)

Splitting the edge is nontrivial because of the landing pad, and we would
currently assert trying to do it.

Differential Revision: https://reviews.llvm.org/D24680
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llvm-svn: 286246