[clang] [Clang] Fixed a crash when __PRETTY_FUNCTION__ or __FUNCSIG__ (clang-cl) appears in the trailing return type of the lambda (PR #122611)

[via cfe-commits]

================
@@ -774,7 +774,15 @@ std::string PredefinedExpr::ComputeName(PredefinedIdentKind IK,
     const FunctionDecl *Decl = FD;
     if (const FunctionDecl* Pattern = FD->getTemplateInstantiationPattern())
       Decl = Pattern;
-    const FunctionType *AFT = Decl->getType()->getAs<FunctionType>();
+
+    // The type may not be fully initialized at this point.
+    // For example, in the trailing return type context of the lambda
+    // expression.
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cor3ntin wrote:

```suggestion
  // Bail out of the type of the function has not been set yet.
  // This can notably happen in the trailing return type of a lambda expression
```

https://github.com/llvm/llvm-project/pull/122611