[clang] [Clang] Use ExtWarn for static local variable in extern inline function (fixes #39524) (PR #166332)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -std=c11 -pedantic-errors -verify %s
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AaronBallman wrote:

This misunderstands the purpose of the issue -- we're accepting the code as an extension and the issue is that we're not correctly identifying it as an extension, so `-pedantic-errors` doesn't reject it. We want the diagnostic in all language modes.

https://github.com/llvm/llvm-project/pull/166332