[clang] [Clang][Sema] Fix crash in CheckUsingDeclQualifier due to diagnostic missing an argument (PR #161277)

[Shafik Yaghmour via cfe-commits]

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@@ -226,7 +227,8 @@ void TrivialButNonPODThroughEllipsis() {
 }
 
 struct HasExplicitConversion {
-  explicit operator bool(); // expected-warning {{explicit conversion functions are incompatible with C++98}}
+  // FIXME I think we should generate this diagnostic in C++20
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shafik wrote:

https://github.com/llvm/llvm-project/issues/161689

https://github.com/llvm/llvm-project/pull/161277