Terminate GORI calculations if a relation is not relevant.

We currently allow VARYING lhs GORI calculations to continue if there is
a relation present in the hope it will eventually better refine a result.
This adds a check that the relation is relevant to the outgoing range
calculation first.  If it is not relevant, stop calculating.

	PR tree-optimization/109192
	* gimple-range-gori.cc (gori_compute::compute_operand_range):
	Terminate gori calculations if a relation is not relevant.
	* value-relation.h (value_relation::set_relation): Allow
	equality between op1 and op2 if they are the same.