[clang] [clang] Enable descriptions for --print-supported-extensions (PR #66715)

[David Spickett via cfe-commits]

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@@ -198,13 +199,20 @@ static int PrintSupportedExtensions(std::string TargetStr) {
   std::unique_ptr<llvm::TargetMachine> TheTargetMachine(
       TheTarget->createTargetMachine(TargetStr, "", "", Options, std::nullopt));
   const llvm::Triple &MachineTriple = TheTargetMachine->getTargetTriple();
+  const llvm::MCSubtargetInfo *MCInfo = TheTargetMachine->getMCSubtargetInfo();
+  const llvm::ArrayRef<llvm::SubtargetFeatureKV> Features =
+    MCInfo->getAllProcessorFeatures();
+
+  llvm::StringMap<llvm::StringRef> llvmDescMap;
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DavidSpickett wrote:

Sure that's got some logic to it, but the code is clearly building a map with data from MCInfo, so it's implicit that it came from the llvm backend. And there isn't another source of data, so it's not like we have an llvm description map and a clang description map and need to know the difference.

Do as you wish it's not a big deal, but if you keep it I think the name should be `LLVMDescMap` to match https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly.

https://github.com/llvm/llvm-project/pull/66715