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

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin approved this pull request.

LGTM with a release note
Please give some time for @AaronBallman to look at this change too

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