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

[Ziqing Luo via cfe-commits]

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@@ -1773,8 +1773,9 @@ def ReadOnlyPlacementChecks : DiagGroup<"read-only-types">;
 // Warnings and fixes to support the "safe buffers" programming model.
 def UnsafeBufferUsageInContainer : DiagGroup<"unsafe-buffer-usage-in-container">;
 def UnsafeBufferUsageInLibcCall : DiagGroup<"unsafe-buffer-usage-in-libc-call">;
+def UnsafeBufferUsageFormatAttr : DiagGroup<"unsafe-buffer-usage-format-attr">;
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ziqingluo-90 wrote:

Can we use `"unsafe-buffer-usage-in-format-attr-call"` for consistency?  [Recently there is `-Wunsafe-buffer-usage-in-static-sized-array` added as well.](https://github.com/llvm/llvm-project/pull/176466)

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