[clang] [Clang] Diagnose UB and emit error when identifier has both internal and external linkage (PR #192116)

[Aaron Ballman via cfe-commits]

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@@ -382,6 +366,10 @@ Improvements to Clang's diagnostics
   code can automatically be made portable to other host platforms that don't
   support backslashes.
 
+- Clang now diagnoses the undefined behavior described in C11 6.2.2p7 where
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AaronBallman wrote:

I think it would make sense to move this to the section about C2y support and cite the later standard, but mention that we reject the code in older language modes as well due to it being undefined behavior.

https://github.com/llvm/llvm-project/pull/192116