[X86][SSE] Vectorize CTTZ + CTTZ_ZERO_UNDEF

[X86][SSE] Vectorize CTTZ + CTTZ_ZERO_UNDEF

Now that we have fast vector CTPOP implementations we can use this to speed up vector CTTZ using the pattern (cttz(x) = ctpop((x & -x) - 1))

Additionally, for AVX512CD that provides lzcnt instructions we can use the pattern (cttz_undef(x) = (width - 1) - ctlz(x & -x))

Differential Revision: http://reviews.llvm.org/D12663

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248091 91177308-0d34-0410-b5e6-96231b3b80d8