[llvm] [ARM] Fix failure to register-allocate CMP_SWAP_64 pseudo-inst (PR #104039)

[Oliver Stannard via llvm-commits]

ostannard wrote:

I've figured out a way to change the CMP_SWAP_64 pseudo-instruction to fix this, avoiding any performance impact on fast-isel or other targets: #106721

https://github.com/llvm/llvm-project/pull/104039