[clang] [Clang] [NFC] Introduce a helper for emitting compatibility diagnostics (PR #132348)

[Aaron Ballman via cfe-commits]

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@@ -178,6 +191,11 @@ multiclass CXXCompat<
                                      "CXX98Compat",
                                      "CXXPre"#std_ver#"Compat"))>,
         DefaultIgnore;
+
+    def : CompatWarningId<
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AaronBallman wrote:

Should we have another layer of abstraction here for C vs C++ vs whatever other language compat warnings?

https://github.com/llvm/llvm-project/pull/132348