[clang] [WIP] Implement `-dump-deserialized-declaration-ranges` flag. (PR #133910)

[Ilya Biryukov via cfe-commits]

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@@ -139,16 +283,17 @@ FrontendAction::CreateWrappedASTConsumer(CompilerInstance &CI,
     return nullptr;
 
   // If there are no registered plugins we don't need to wrap the consumer
-  if (FrontendPluginRegistry::begin() == FrontendPluginRegistry::end())
-    return Consumer;
+  if (FrontendPluginRegistry::begin() == FrontendPluginRegistry::end()) {
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ilya-biryukov wrote:

Also, we still don't want to create a `MultiplexConsumer` if our flag wasn't specified, right?
So I think we need to update this code anyhow.

https://github.com/llvm/llvm-project/pull/133910