Remove most of the uses of SDOperandPtr, usually replacing it with a

simple const SDOperand*, which is what's usually needed.

For AddNodeIDOperands, which is small, just duplicate the function to
accept an SDUse*.

For SelectionDAG::getNode - Add an overload that accepts SDUse* that
copies the operands into a temporary SDOperand array, but also has
special-case checks for 0 through 3 operands to avoid the copy in
the common cases.

llvm-svn: 53183