f1eed011b4
5221634 (Do not trigger UB during AffineExpr parsing) noticed that divideCeilSigned and divideFloorSigned would overflow when Numerator = INT_MIN, and Denominator = -1. This observation has already been made by DynamicAPInt, and it has code to check this. To avoid checks in multiple callers, centralize this query in MathExtras, and change divideCeilSigned/divideFloorSigned to assert on overflow.