[llvm] [LLVM-C] Upstream `LLVMBuildAtomicLoad/Store` from rustc (PR #162450)

[Nikita Popov via llvm-commits]

nikic wrote:

Hm, do we really need these? Aren't these just combinations of LLVMBuildLoad2/LLVMBuildStore + LLVMSetOrdering (+ LLVMSetAtomicSingleThread if necessary)?

The calling code already sets the alignment separately: https://github.com/rust-lang/rust/blob/5767910cbcc9d199bf261a468574d45aa3857599/compiler/rustc_codegen_llvm/src/builder.rs#L649-L650 So I don't think there is a strong reason to integrate setting the ordering into one C API call.

https://github.com/llvm/llvm-project/pull/162450