tree-optimization/104519 - adjust PR100499 niter fix

tree-optimization/104519 - adjust PR100499 niter fix

The following adjusts the PR100499 niter fix to use the appropriate
types when checking whether the difference between the final and base
values of the IV are a multiple of the step.  It also gets rid of
an always false condition in multiple_of_p which lead me to a
wrong solution first.

2022-02-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/104519
	* fold-const.cc (multiple_of_p): Remove never true condition.
	* tree-ssa-loop-niter.cc (number_of_iterations_ne): Use
	the appropriate types for determining whether the difference
	of final and base is a multiple of the step.

	* gcc.dg/torture/pr104519.c: New testcase.