[llvm] [NFC][CodingStandard] Deprecate use of void casts to suppress warnings (PR #142850)

[Florian Mayer via llvm-commits]

fmayer wrote:

Just confirming that this means something like

```
void f(int x) {
#ifdef XYZ
  (void)x;
  [...]
#else
  [do something with x]
```

becomes

```
void f([[maybe_unused]] int x) {
#ifdef XYZ
  [...]
#else
  [do something with x]
```


https://github.com/llvm/llvm-project/pull/142850