[LV] Preserve LoopInfo when store predication is used

This was a latent bug that got exposed by the change to add LoopSimplify
as a dependence to LoopLoadElimination.  Since LoopInfo was corrupted
after LV, LoopSimplify mis-compiled nbench in the test-suite (more
details in the PR).

The problem was that when we create the blocks for predicated stores we
didn't add those to any loops.

The original testcase for store predication provides coverage for this
assuming we verify LI on the way out of LV.

Fixes PR26952.

llvm-svn: 263565