[clang] [-Wunsafe-buffer-usage] Fix a bug and suppress libc warnings for C files (PR #109496)

[via cfe-commits]

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@@ -2549,6 +2549,7 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
   DiagnosticOptions &DiagOpts = Diags.getDiagnosticOptions();
 
   // UnsafeBufferUsage analysis settings.
+  bool IsCXXLang = S.getLangOpts().CPlusPlus;
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jkorous-apple wrote:

Nit: it doesn't feel like we need a variable for that.

https://github.com/llvm/llvm-project/pull/109496