[clang] [Clang][Sema] Don't assert on friend declarators with an empty name (PR #223213)

[Younan Zhang via cfe-commits]

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@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify %s
+
+template <template <typename> class C> struct S { // expected-note {{template is declared here}}
+    friend C(); //expected-error {{cannot specify deduction guide for template template parameter 'C'}}
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zyn0217 wrote:

Why do we diagnose it as a deduction guide?

https://github.com/llvm/llvm-project/pull/223213