[libc-commits] [libc] [libc] Enable `-Wunused` and clean up found instances (PR #96949)

[Rajveer Singh Bharadwaj via libc-commits]

Rajveer100 wrote:

@michaelrj-google
Just noticed this had been lying around for a while, I noticed that regardless of adding the compile flag, `-Wunused` error is enabled, I checked this by adding few unused instances like (int some_var = 0).

It was not triggered for the the specific case:

```c++
  FPBits sk_cy(sin_k_cos_y.hi);
  FPBits ck_sy(cos_k_sin_y.hi);
```

But works for:

```
  FPBits sk_cy;
```

Considering this, I think this PR and the linked issue can be closed?

https://github.com/llvm/llvm-project/pull/96949