Allow more precision when querying from fold_const.

fold_const::expr_not_equal_to queries for a current range, but still uses
the old value_range class.  This is causing it to miss opportunities when
ranger can provide something better.

	PR tree-optimization/83072
	PR tree-optimization/83073
	PR tree-optimization/97909
	gcc/
	* fold-const.c (expr_not_equal_to): Use a multi-range class.

	gcc/testsuite/
	* gcc.dg/pr83072-2.c: New.
	* gcc.dg/pr83073.c: New.