[clang] [clang][Parse] Fix __extension__ not silencing diagnostics (PR #221623)

[Richard Patel via cfe-commits]

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@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 %s -fsyntax-only -pedantic -verify -std=c17
+// RUN: %clang_cc1 %s -fsyntax-only -pedantic -verify -std=c2y
+// RUN: %clang_cc1 %s -fsyntax-only -pedantic -verify -x c++ -std=c++17
+
+// expected-no-diagnostics
+
+int f(int);
+
+void cond(int a) {
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riptl wrote:

@AaronBallman 23.1.0 is not affected, but Clang 24 (trunk) is.
<img width="1137" height="712" alt="Screenshot 2026-09-12 at 07 37 24" src="https://github.com/user-attachments/assets/69d29a60-8dad-4142-993f-d1aa66000871" />


https://github.com/llvm/llvm-project/pull/221623