Add relation to unsigned right shift.

If the first operand and the shift value of a right shift operation are both
>= 0, then we know the LHS of the operation is <= the first operand.

	PR tree-optimization/96707
	gcc/
	* range-op.cc (operator_rshift::lhs_op1_relation): New.

	gcc/testsuite/
	* g++.dg/pr96707.C: New.