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

[Rajveer Singh Bharadwaj via libc-commits]

Rajveer100 wrote:

Also, I see some errors when doing `ninja -C build check-libc`:

```Shell
Undefined symbols for architecture arm64:
  "__llvm_libc_19_0_0_git::quick_exit(int)", referenced from:
      __llvm_libc_19_0_0_git::BlockStore<int, 4ul, false>::pop_back() in blockstore_test.cpp.o
      __llvm_libc_19_0_0_git::BlockStore<int, 4ul, false>::get_last_blocks() in blockstore_test.cpp.o
      __llvm_libc_19_0_0_git::BlockStore<int, 4ul, true>::pop_back() in blockstore_test.cpp.o
ld: symbol(s) not found for architecture arm64
```

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