tree-optimization/117574 - bougs niter lt-to-ne

tree-optimization/117574 - bougs niter lt-to-ne

When trying to change a IV from IV0 < IV1 to IV0' != IV1' we apply
fancy adjustments to the may_be_zero condition we compute rather
than using the obvious IV0->base >= IV1->base expression (to be
able to use > instead of >=?).  This doesn't seem to go well.

	PR tree-optimization/117574
	* tree-ssa-loop-niter.cc (number_of_iterations_lt_to_ne):
	Use the obvious may_be_zero condition.

	* gcc.dg/torture/pr117574-1.c: New testcase.

(cherry picked from commit ff5a14abeb31cd6bd0ca55e7043d05c8141a8c7f)