Change integral divide by zero to produce UNDEFINED.

Change integral divide by zero to produce UNDEFINED.

Instead of VARYING, we can get better results by treating divide by zero
as producing an undefined result.

	gcc/
	* range-op.cc (operator_div::wi_fold): Return UNDEFINED for [0, 0] divisor.

	gcc/testsuite/
	* gcc.dg/tree-ssa/pr61839_2.c: Adjust.