[clang] [HLSL][NFC] Refactor HLSLExternalSemaSource (PR #131032)

[Justin Bogner via cfe-commits]

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@@ -21,20 +21,15 @@ class NamespaceDecl;
 class Sema;
 
 class HLSLExternalSemaSource : public ExternalSemaSource {
+private:
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bogner wrote:

The default visibility in `class` is private, so this doesn't do anything

https://github.com/llvm/llvm-project/pull/131032