[clang] Add new flag -Wreturn-mismatch (PR #82872)

[Bhuminjay Soni via cfe-commits]

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@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -Wno-return-type -Wreturn-mismatch -fsyntax-only -verify %s
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11happy wrote:

done

https://github.com/llvm/llvm-project/pull/82872