AVX-512: Added implementation of CONCAT_VECTORS for v8i1 vectors (by Alexey Bader).
Added implementation of "truncate" from integer type (i64/i32/i16/i8) to i1.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197482 91177308-0d34-0410-b5e6-96231b3b80d8