[clang] [clang] Catch missing format attributes (PR #70024)

[Aaron Ballman via cfe-commits]

================
@@ -0,0 +1,223 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wmissing-format-attribute %s
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <uchar.h>
+#include <wchar.h>
----------------
AaronBallman wrote:

Our test files should be hermetic and not rely on anything from the test system itself. `stdarg.h` is fine because we provide that as part of Clang, but the rest are all being pulled from the system. You should use forward declarations or other tricks so that these can be removed.

https://github.com/llvm/llvm-project/pull/70024