scalarizePHI needs to insert the next ExtractElement in the same block
as the BinaryOperator, *not* in the block where the IRBuilder is currently
inserting into. Fixes a bug where scalarizePHI would create instructions
that would not dominate all uses.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182639 91177308-0d34-0410-b5e6-96231b3b80d8