Not enough to notice. It's being sucked into the cylinders or the crankcase very slowly because it's a small leak. A cracked block would lose water like crazy because that's a crack in the water jacket itself.
I've seen this before, and it's always the same. The way to tell for sure is to do a compression test on each cylinder. You'll get a bad reading where the leak is in the cylinder head gasket. You'll probably know by looking at the spark plugs when you pull them out to do the test which one(s) it is. It could have failed in the head gasket just between the water passages and the oil passages, without traveling to the cylinders, but usually once it fails it fails to the cylinder.
But that's water in your oil, and it only gets into it a couple of ways. The head gasket is the most common. I don't want to think about the other problems, which is a crack somewhere, either in the head or in the block.
