Fix for PR17073 ( http://llvm.org/pr17073 ), simplifycfg illegally hoists an operation in a phi node that can trap.

This patch adds to an existing loop over phi nodes in SimplifyCondBranchToCondBranch() to check for trapping ops and bails out of the optimization if we find one of those.

The test cases verify that trapping ops are not hoisted and non-trapping ops are still optimized as expected.