[clang] Fix auto with type in modern C++ (PR #208552)

[Vlad Serebrennikov via cfe-commits]

================
@@ -1704,14 +1704,16 @@ namespace cwg395 { // cwg395: 3.0
 
 namespace cwg396 { // cwg396: 3.0
   void f() {
-    auto int a();
-    // since-cxx11-error at -1 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}}
-    // expected-error at -2 {{illegal storage class on function}}
+    auto int a(); // #cwg396-a
+    // cxx98-error@#cwg396-a {{illegal storage class on function}}
+    // since-cxx11-error@#cwg396-a {{'auto' cannot be combined with a type specifier}}
+    // since-cxx11-warning@#cwg396-a {{empty parentheses interpreted as a function declaration}}
+    // since-cxx11-note@#cwg396-a {{replace parentheses with an initializer to declare a variable}}
     int (i); // #cwg396-i
-    auto int (i);
-    // since-cxx11-error at -1 {{'auto' storage class specifier is not permitted in C++11, and will not be supported in future releases}}
-    // expected-error at -2 {{redefinition of 'i'}}
-    //   expected-note@#cwg396-i {{previous definition is here}}
+    auto int (i); // #cwg396-auto-i
+    // cxx98-error@#cwg396-auto-i {{redefinition of 'i'}}
+    // cxx98-note@#cwg396-i {{previous definition is here}}
----------------
Endilll wrote:

```suggestion
    //   cxx98-note@#cwg396-i {{previous definition is here}}
```

https://github.com/llvm/llvm-project/pull/208552