Fix for sanitizer crash introduced in r209049

This patch fixes 3 issues introduced by r209049 that only showed up in on
the sanitizer buildbots. One was a typo in a compare. The other is a check to
confirm that the single differing value in the two incoming GEPs is the same
type. The final issue was the the IRBuilder under some circumstances would
build PHIs in the middle of the block.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209065 91177308-0d34-0410-b5e6-96231b3b80d8