re PR target/82274 (__builtin_mul_overflow fails to detect overflow for int64_t when compiled with -m32)

	PR target/82274
	* internal-fn.c (expand_mul_overflow): If both operands have
	the same highpart of -1 or 0 and the topmost bit of lowpart
	is different, overflow is if res <= 0 rather than res < 0.

	* libgcc2.c (__mulvDI3): If both operands have
	the same highpart of -1 and the topmost bit of lowpart is 0,
	multiplication overflows even if both lowparts are 0.

	* gcc.dg/pr82274-1.c: New test.
	* gcc.dg/pr82274-2.c: New test.

From-SVN: r253734