Reverted r332654 as it has broken some buildbots and left unfixed for a long time.

The introduced problem is:
llvm.src/lib/Transforms/Vectorize/VPlanVerifier.cpp:29:13: error: unused function 'hasDuplicates' [-Werror,-Wunused-function]
static bool hasDuplicates(const SmallVectorImpl<VPBlockBase *> &VPBlockVec) {
            ^

llvm-svn: 332747