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

[Aaron Ballman via cfe-commits]

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@@ -1,5 +1,5 @@
 // XFAIL: target=aarch64-pc-windows-msvc
-// RUN: %clang_cc1 -Wno-return-type -Wno-unused-value -emit-llvm %s -w -o - | FileCheck %s
+// RUN: %clang_cc1 -Wno-return-type -Wno-return-mismatch -Wno-unused-value -emit-llvm %s -w -o - | FileCheck %s
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AaronBallman wrote:

Similarly, why is this change required -- I would have assumed that `-Wno-return-type` was sufficient to silence both. (Same question applies to `return-silent.c`.)

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