[clang] [libcxx] [Clang] Add __common_type builtin (PR #99473)

[via cfe-commits]

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@@ -2282,6 +2282,10 @@ class Sema final : public SemaBase {
   /// Check to see if a given expression could have '.c_str()' called on it.
   bool hasCStrMethod(const Expr *E);
 
+  // Check whether a type member 'Type::Name' exists, and if yes, return the
+  // type. If there is no type, the QualType is null
+  QualType getTypeMember(StringRef Name, QualType Type);
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Sirraide wrote:

```suggestion
  /// Check whether a type member 'Type::Name' exists, and if yes, return the
  /// type. If there is no type, the QualType is null
  QualType getTypeMember(QualType Type, StringRef Name);
```
This should probably be a doc comment.

Nit: since that entails touching this file anyway: I’d also swap the two parameters because reading `Type::Name` in the comment but having the first parameter be `Name` and the second `Type` makes it a bit harder to read, but that might also just be a me problem ;Þ

https://github.com/llvm/llvm-project/pull/99473