[clang] clang should have a warning to disallow re-externs (PR #109714)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I appreciate the idea, but I don't think it's a diagnostic we'd want to accept in Clang itself. We typically don't want to add new default-off diagnostics because there's plenty of evidence that they aren't enabled often enough to warrant having them. But also, this is really something that's better left to a tool other than the compiler. For example, Clang's static analyzer has cross-translation unit analysis support (https://clang.llvm.org/docs/analyzer/user-docs/CrossTranslationUnit.html) which seems like it would be a better fit.

https://github.com/llvm/llvm-project/pull/109714