Allow target intrinsics that return multiple values, i.e., struct types,

Allow target intrinsics that return multiple values, i.e., struct types,
in SelectionDAGLowering::visitTargetIntrinsic.

This removes a bit of special-case code for vector types.  After staring
at it for a while, I managed to convince myself that it is not necessary.
The only case where TLI.getValueType() differs from MVT::getMVT is for iPTR,
so this code could potentially make a difference for a vector of pointers.
But, it looks like that is not supported.  Calling TLI.getValueType() on
a vector of pointers leads to the following sequence of calls:

TargetLowering::getValueType
MVT::getMVT
MVT::getVectorVT(iPTR, num elements)
MVT::getExtendedVectorVT
MVT::getTypeForMVT for iPTR
assertion fails "Type is not extended!"

So, unless I'm really missing something, this bit of code is irrelevant to
the current version of LLVM, which is consistent with the fact that I don't
see this code in other similar places.

llvm-svn: 77747