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

[David Spickett via llvm-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();
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DavidSpickett wrote:

I just thought of one more thing. What happens here if the build was configured without the target backend enabled?

For example if CMake was configred with `-DLLVM_TARGETS_TO_BUILD=ARM`, and you ask for the RISC-V extensions, does clang crash?

Though that is an unusual thing to do, but it is possible since clang knows about all possible triples even without a target backend. And besides that, clang shouldn't crash anyway. Simplest solution is to pass an empty description map I think, and add a test for that situation.

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