[llvm] [X86] Prefer `lock or` over mfence (PR #106555)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

```
Failed Tests (2):
  LLVM :: Transforms/Inline/X86/inline-target-cpu-i686.ll
  LLVM :: Transforms/Inline/X86/inline-target-cpu-x86_64.ll
```

https://github.com/llvm/llvm-project/pull/106555