[clang] [Clang][Sema] fix outline member function template with default align crash (PR #78400)

[Erich Keane via cfe-commits]

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@@ -3051,6 +3051,7 @@ bool Sema::SubstDefaultArgument(
     //   default argument expression appears.
     ContextRAII SavedContext(*this, FD);
     std::unique_ptr<LocalInstantiationScope> LIS;
+    auto NewTemplateArgs = TemplateArgs;
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erichkeane wrote:

Don't use auto here.

https://github.com/llvm/llvm-project/pull/78400