[clang] [C++20][Modules] Restore inliness of constexpr/consteval functions defined in-class (PR #109470)

[via cfe-commits]

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@@ -9760,8 +9760,8 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   if (getLangOpts().CPlusPlus) {
     // The rules for implicit inlines changed in C++20 for methods and friends
     // with an in-class definition (when such a definition is not attached to
-    // the global module).  User-specified 'inline' overrides this (set when
-    // the function decl is created above).
+    // the global module). This does not affect declarations, that are already
+    // inline, for example due being declared `inline` or `consteval`
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cor3ntin wrote:

```suggestion
    // the global module). This does not affect declarations that are already
    // inline (whether explicitly or implicitly by being declared constexpr, etc)
```

https://github.com/llvm/llvm-project/pull/109470