Merging r296698:

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r296698 | rnk | 2017-03-01 17:41:12 -0500 (Wed, 01 Mar 2017) | 10 lines

[Constant Hoisting] Avoid inserting instructions before EH pads

Now that terminators can be EH pads, this code needs to iterate over the
immediate dominators of the EH pad to find a valid insertion point.

Fix for PR32107

Patch by Robert Olliff!

Differential Revision: https://reviews.llvm.org/D30511
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llvm-svn: 299670