I just noticed (while looking at JDK-8372800) that I made a little error in JDK-8372188 refactor, which made GetAndSet-acquire instruction cost twice as high. The usual cost for acquire versions are twice as low, likely to be selected instead of non-acquire versions.

This bug happened as I "simplified" stencils at some point by dropping some arguments and renumbering the remaining ones. This is one place where I apparently forgot to renumber one usage. Seen no real bugs because of this mishap, but it would be good to fix it in case we see issues later. I also looked at stencils again, and I think there are no other argument-index problems like this anywhere else.