Utilize op1 == op2 when invoking range-ops folding.

Utilize op1 == op2 when invoking range-ops folding.

If there exists an equivalence relationship between op1 and op2,
any binary operation can be broken into individual operations and
unioned if there are sufficently few elements in the set.

	PR tree-optimization/108359
	gcc/
	* range-op.cc (range_operator::wi_fold_in_parts_equiv): New.
	(range_operator::fold_range): If op1 is equivalent to op2 then
	invoke new fold_in_parts_equiv to operate on sub-components.
	* range-op.h (wi_fold_in_parts_equiv): New prototype.

	gcc/testsuite/
	* gcc.dg/pr108359.c: New.