[clang] [clang] Build argument string for clang::warn_unused_result (PR #148090)

[via cfe-commits]

zebullax wrote:

Seems 🟢 
```
➜  clang git:(patch-1) ✗ build/bin/llvm-lit -sv  clang-p2996/clang/test/SemaCXX/warn-unused-result.cpp
...

Testing Time: 0.40s

Total Discovered Tests: 1
  Passed: 1 (100.00%)
```


https://github.com/llvm/llvm-project/pull/148090