The way that splitInnerLoopHeader splits blocks requires that
the induction PHI will be the first PHI in the inner loop
header. This makes sure that is actually the case when there
are both IV and reduction phis.
Differential Revision: https://reviews.llvm.org/D38682
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316261 91177308-0d34-0410-b5e6-96231b3b80d8
