As part of enhancing atomic operations in the ARM backend, we need to
extend the Ops array in AtomicSDNode.
This array is a private member of AtomicSDNode, so it's only
accessible within 85 lines of code, none of which have anything to do
with its size. Therefore, increasing the size of Ops shouldn't at all
affect the behaviour of LLVM, we supposed.
Much to our surprise, this isn't as trivial.
Even this innocuous change: