[clang] [clang-repl] Fix duplicate definition error for symbols in C mode (PR #164597)

[Vassil Vassilev via cfe-commits]

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@@ -1447,6 +1447,10 @@ void Sema::ActOnEndOfTranslationUnit() {
     if (!VD || VD->isInvalidDecl() || !Seen.insert(VD).second)
       continue;
 
+    if (PP.isIncrementalProcessingEnabled() &&
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vgvassilev wrote:

Let's try cleaning `TentativeDefinitions` instead and add tests.

https://github.com/llvm/llvm-project/pull/164597