[llvm] [clang] [clang-tools-extra] [X86] Use plain load/store instead of cmpxchg16b for atomics with AVX (PR #74275)

[James Y Knight via cfe-commits]

jyknight wrote:

@RKSimon: I'm not sure if you intended your comment to be a blocker; I was about to press the merge button when you commented (and would still wish to now).

https://github.com/llvm/llvm-project/pull/74275