[clang] Suppress octal literal diagnostics from system macros (PR #192481)

[Vlad Serebrennikov via cfe-commits]

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@@ -166,5 +166,27 @@ void foo() {
 }
 #endif
 
+#172 "system_header.c" 3
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Endilll wrote:

It feels strange that a header would have `.c` extension. Also, what exactly makes Clang think this is a system header?

https://github.com/llvm/llvm-project/pull/192481