Lower AVX v4i64->v4i32 truncate to one shuffle.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202996 91177308-0d34-0410-b5e6-96231b3b80d8
ConstantFolding: Also fold the vector overloads of our math intrinsics.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202997 91177308-0d34-0410-b5e6-96231b3b80d8