[llvm] [Targets] Migrate from atomic_load_8/16/32/64 to atomic_load_nonext_8/16/32/64. NFC (PR #137428)

[Craig Topper via llvm-commits]

topperc wrote:

> Will they be reintroduced with new semantics or why remove them?

I don't plan to reintroduce them. I guess I can leave them as dead code to avoid breaking out of tree targets?

https://github.com/llvm/llvm-project/pull/137428