[clang] [-Wunsafe-buffer-usage] Separate flag for format-attributed functions (PR #175749)

[via cfe-commits]

llvmbot wrote:

<!--IGNORE-->
Failed to cherry-pick: 3d90b7a2d7333ead420b18baece183249404329a

https://github.com/llvm/llvm-project/actions/runs/21164144924

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

https://github.com/llvm/llvm-project/pull/175749