re PR middle-end/91450 (__builtin_mul_overflow(A,B,R) wrong code if product < 0, *R is unsigned, and !(A&B))

	PR middle-end/91450
	* internal-fn.c (expand_mul_overflow): For s1 * s2 -> ur, if one
	operand is negative and one non-negative, compare the non-negative
	one against 0 rather than comparing s1 & s2 against 0.  Otherwise,
	don't compare (s1 & s2) == 0, but compare separately both s1 == 0
	and s2 == 0, unless one of them is known to be negative.  Remove
	tem2 variable, use tem where tem2 has been used before.

	* gcc.c-torture/execute/pr91450-1.c: New test.
	* gcc.c-torture/execute/pr91450-2.c: New test.

From-SVN: r278437