Add support for scalarizing cttz_zero_undef

Follow up to r214266. Add missing case in ScalarizeVectorResult() for
cttz_zero_undef.

Differential Revision: http://reviews.llvm.org/D4813


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215330 91177308-0d34-0410-b5e6-96231b3b80d8