Add lhs_op1 relation to pointer_plus

Add lhs_op1 relation to pointer_plus

When prange was split from irange, the functionality of lhs_op1_relation
did not get ported.  This patch adds that functionality back, and is
also good example of how to add new dispatch patterns to range-ops
as lhs_op1_relation had no prange/prange/irange combination.

	* range-op-ptr.cc (range_operator::lhs_op1_relation): Add
	prange/prange/irange (PPI) default.
	(pointer_plus_operator::lhs_op1_relation): New.
	* range-op.cc (range_op_handler::lhs_op1_relation): Add RO_PPI case.
	* range-op.h (range_op_handler::lhs_op1_relation): Add prototype.