[clang] Add check in SemaChecking for multiple unsequenced volatile accesses (PR #180955)

[Aaron Ballman via cfe-commits]

================

----------------
AaronBallman wrote:

```suggestion
    x = v1 * v1;       // cxx11-warning {{unsequenced accesses to volatile qualified 'v1'}}
```
?

https://github.com/llvm/llvm-project/pull/180955