[X86] Add test cases to cover the path in VectorLegalizer::ExpandLoad for non-byte...

[X86] Add test cases to cover the path in VectorLegalizer::ExpandLoad for non-byte sized loads where bits from two loads need to be concatenated.

If the scalar type doesn't divide evenly into the WideVT then the code will need to take some bits from adjacent scalar loads and combine them.

But most of our testing is for i1 element type which always divides evenly.

llvm-svn: 354653