[llvm] [llvm][NFC] Autoupdater AMD intrinsic detection (PR #73331)

[Nathan Sidwell via llvm-commits]

urnathan wrote:

You're right, I'd got too fixated on StringSwitch.  Here's an update just addressing the 'atomic' ops, where the prefix check can help.

https://github.com/llvm/llvm-project/pull/73331